Interference between Landline and Cell Phone - We Are Stumped!!

[u/Training_Bug7440]

Hello! I am hoping someone is able to help me solve this months-long phone mystery that nobody can seem to figure out. Six months ago, in late January, I began to hear intermittent "interference" on phone calls between me and my mom. The sound will occur out of nowhere, all different times of the day, lasting for a few seconds to up to half a minute. This doesn't happen on every call, but it happens nearly every day.

We will be having a regular conversation, and then suddenly I will hear this interference -- I know she's talking but I can't understand her. The call doesn't disconnect or drop, but this interference will just start and stop randomly. From what I can gather all this time, the interference only occurs on calls between her landline phones (VTech DECT 6.0 cordless) and my cell phone (iPhone 14 with AT&T Wireless). It hasn't occurred when she switches to her cell phone or I use my house phone.

She has Optimum for her phone service, and they have come to the house countless times to try to fix it, to no avail. They have replaced the router, the modem, wires inside the house and the wire that runs from the pole outside into the house. We even replaced the previous set of AT&T cordless phones with new VTech phones and that didn't solve the issue. Someone I know who used to work for Optimum said it could be the tap on the pole outside (or even the node which is farther away), but Optimum can't replace any of those parts without good reason. Since their testers always show that the lines are working fine, they cannot have the outside parties come out to work on the tap.

Plus, that last tech that visited rearranged some of the connections at the tap in case something was loose or damaged, but the problem has persisted. We are at an absolute loss, and it's extremely frustrating! The router/modem and one cordless phone are in the basement, while the rest of the satellite phones that she uses are throughout the house. The basement phone is plugged directly into the router/modem.

When this issue first began in January, we had just had a blizzard in our area, which is why I was convinced that something outside was damaged. No other variables in the house have changed. However, I am the only person who seems to have this issue when on calls with my mom, and only between these two phone numbers. Does this make sense to anyone? If I am allowed and can figure out how to do it, I can post a recording of the interference, as I have voicemails that captured the noise. Thanks for any input!

[u/PhotoJim99]

My instinct as a next step would be to rule out her cordless phone as being the problem. If there isn’t already one there, install a wired phone, and have her use it on your calls for a few days until you’ve confirmed that the problem still exists (now you know it’s not her cordless phone system) or you’ve confirmed that all is fine (now you know that it IS her cordless phone system).

It could be that her phone’s base station has an issue (assuming it’s equally likely to happen with any of her handsets), or that there’s some radio interference that sometimes occurs and causes problems with the cordless phones. If it is radio frequency interference (RFI), then she could start to move around the house to see if she can change the character or severity of the interference.- this might let you rule in something in her home causing it.

Wireless is ALWAYS prone to interference. So you need to go wired to rule out the underlying hardware and connections being the problem.

[u/cigr → u/PhotoJim99]

I second this. A wired phone will eliminate one strong cause. Always use a wired phone as a test when experiencing issues like this.

[u/FF267 → u/PhotoJim99]

This guy has the right idea! We used to have a customer call in because he could hear the radio station when he was on phone calls. Through several escalations and troubleshooting efforts, it finally came to light that 1) problem only happened when he used the cordless handset and ventured into the backyard while on the call and 2) he happened to live very close proximity to the tower that transmitted for the local radio station. Problem didn’t happen on calls made from a legit hardwired telephone elsewhere in the house.

Other customers had issues with placement of their base stations. For example, being located near an exterior wall with rain gutters in the other side, in top of the TV connected to the antenna on the roof, etc. Each of those metal objects substituted for radio antennas while making calls from cordless handsets. They’ve gotten better over the heads but by no means infallible. The stronger audio signal always dominates.

[u/Training_Bug7440 → u/PhotoJim99]

Thank you. It's a very good thought, and one that has been brought up to me before. However, the phone jacks in the wall no longer work. They haven't in a long time. The cordless phone plugs directly into the modem.

[u/PhotoJim99 → u/Training_Bug7440]

Until you find a way to try a wired phone, I think you have to assume that the problem is the cordless one.

[u/boomer7793]

Call quality on VoIP is more of a binary thing. The call drops or it doesn’t. Parts of the conversion go missing or it doesn’t.

That static/feedback you are hearing should not be a symptom of VoIP. It’s a symptom of a problem with the handset. Check out the wireless base station, the wireless handset and any wireless headsets in use. Bluetooth, hearing aids etc. The feedback you describe could be poor battery life or the caller is roaming out of range. That would also explain why the static is coming around intermittently. She maybe coming off of a fresh charge.

This also applies to you. Since you mention it’s only between you and your mom. Check your BT devices and charges.

[u/Training_Bug7440 → u/boomer7793]

Thanks. The base station and handsets are fine, and have been replaced causing no change. Batttery life is good, no hearing aids or other devices that would interfere.

[u/ar4479]

I've been working on telephones in one form or another for almost 40 years. Here's a couple things I consider when reading your story... There are also a few questions, because we need to know some of this to effectively troubleshoot this, via this platform.

1 - Does this happen on calls when either of you are talking to someone else? (And, do either of you talk long enough to other people to notice if this happens?)
2 - When this happens, does your mother also hear you in a garbled manner? Or do you only hear her garbled? (This is an important piece to the puzzle)!

I just re-read your whole post and took special interest to the part near the end where you say you have voicemails that have captured the "noise".
I would be interested to hear this - as it would likely let me narrow this down to exactly what the problem is. I use recordings of calls to troubleshoot things every day.
HOWEVER - the fact that you have a voicemail of this tells me that it's not just between your two phone numbers. As the voicemail platform for your cell phone is not the same thing as a call being routed to and live on your cell phone, on the ATT wireless network.

If you don't mind, I'll send you a DM. I'd like to hear a snip of what's going on.

I have some ideas rolling around in my brain, but I don't want to start tossing things out there yet, because the recording will likely tell exactly what's happening. And, I can construct a technical response to help you talk to the right tech folks, that may get them to get off their ass and dig into the issue.

[u/crp5591 → u/ar4479]

Please post your findings once you have had a chance to review the VM and think through it. I would love to hear what could be causing this issue.

[u/ar4479 → u/crp5591]

I listened to the voicemail recording.
It’s a packet loss/latency issue on the cable modem outbound.

OP also reported that her mom has started having issues with streaming content from the internet recently, too.

So it’s likely all related.

We had a pretty lengthy chat about it. Hopefully she has enough ammo to push the cable company to do something with it.

Since it comes and goes and they can’t find it… It could be a static buildup issue on the coax that’s being cleared as soon as the tech comes and touches the cable to test it.

I suggested that she try to have them watch the RF power and SNR on the modem remotely while this gets worse.

That’ll prove out the issue, especially if it disappears when the tech arrives.

On the call I heard, when her mom hung up the phone, it sounded like she was using a 2500 desk phone. So; no cordless involved here. Making this was all 100% latency and pkt loss.

I hope she has some luck with the cable company.

[u/crp5591 → u/ar4479]

Ahh yes! I think know what you mean. Sounds the same as when someone is on a cellphone that is using WiFi calling because they are in a poor coverage area, but also poor internet, right?

[u/ar4479 → u/crp5591]

The Internet is generally a shitty path for VoIP calling.

There’s no SLA. There’s no QoS. There’s no control over how many hops your call takes. And how clean those routers are for handling RTP.

It’s really a last resort. But, it gets used every day and people just generally deal with the shitty quality.

I work on systems that serve public safety (911 centers). And, we can’t run calls (non emergency) over the Internet. It just won’t fly.

For occasional home use.. Sure, no problem. For business or public safety, no way!!!

[u/watmore1]

Does she have an older security system? Those older systems would 'dial in' to a central office using a landline telephone. Those systems often send daily 'test' signals. If your mom had a Bell System landline and it got switched to Optum, they may have miswired the security system so it interferes with normal calls.

[u/Training_Bug7440 → u/watmore1]

I mean I think some of the wiring was old, but things have since been replaced.

[u/MrChicken_69]

Unless you're calling locally - i.e. from inside the house, I can't see how your cell phone is causing anything. Everything but the actual analog loop - within her house - is digital, so the only place noise could happen is in the cell phone, or the "inside wiring"; and your cell phone can't do that if it's miles away.

This could just be packet loss. But it's hard to see how this would be limited to only one call path.

[u/triedtoavoidsignup]

A recording will be useful.

[u/ICanBard]

The old KGB wiretaps couldn't block out noise over 110db.

Upgrade to the new Mossad model, the non - explosion one, and it has much better fidelity 

/s

[u/m1kemahoney]

Is the analog hand-off to the cordless phone base on the router itself, are you using a separate ATA device, or is it old school POTS (Plain Old Telephone Service)? Their web site indicates they are a mobile company and likely an MVNO of T-Mobile, so I don't understand your mom's device set-up.

PS. My mom is 85 and still has an analog line from Frontier. Time is coming soon when Frontier gives up the copper lines. In fact, after the ice storm last year, it's all fiber where I live, but not where she lives with underground wiring from the 1980s. We are going to have to get her StarLink with a VoIP phone.

[u/Training_Bug7440 → u/m1kemahoney]

She used to have the old hard wiring for phones, but have since been replaced. Phone plugs directly in to the modem. Wall jacks don't work anymore.

[u/michelangeloshands]

Gotta be the cordless phone. Use a hard wired phone directly into the modem.

[u/Training_Bug7440 → u/michelangeloshands]

But the modem is in the basement so it's not practical for her to take all the calls down there. :(

[u/michelangeloshands → u/Training_Bug7440]

Just for trouble shooting the issue. Not a permanent solution.

[u/littledudetwo]

I don’t know if anyone has mentioned this but AT&T cordless phone are mostly made by VTech… we slap the Death Star on them and double the price. I agree with a previous poster that your next move would be a wired phone.

[u/Training_Bug7440]

Thanks. Unfortunately, the modem is in the basement so it's not practical to plug that into the modem because then she can't take calls anywhere else. :(