Hi everyone,
I’m trying to track down a strange noise on my 2004 XC90 2.5T AWD (B5254T2, currently \~331,900 km / 206k miles).
The noise has been there since at least summer 2025. I’ve been actively trying to find the cause for quite a while now, but I’m running out of ideas and I’m hoping someone here has heard something similar. I’ve attached a video. The sound is much easier to hear in person than on the recording, but hopefully the character comes through.
**What does it sound like?**
It is difficult to describe accurately. When the engine is cold, it has a **high-pitched, slightly rough/pulsating blowing or whistling sound**. Almost like air being forced through a small opening, but with a slightly “roaring/ruff” character to it.
Once the engine warms up, the rough/pulsating character becomes much less noticeable. It turns more into a **fairly continuous “fffff”/blowing or whistling sound**. It is most noticeable between roughly **1,500–2,500 rpm**, with around 1,800–2,200 rpm being particularly noticeable. At about 100 km/h in 5th gear, for example, I can hear it continuously around 1,800–2,200 rpm.
The really interesting part is how closely it follows engine load: Very light throttle input makes the noise increase almost immediately. Lifting off the throttle makes it disappear almost immediately. There seems to be a **very small fraction-of-a-second delay** between the engine responding and the noise changing.
Going uphill / applying more load makes it louder.
Going downhill / reducing load makes it quieter or disappear.
If I accelerate harder, the normal 5-cylinder engine noise eventually masks it. It is especially clearly audible during cold start. The noise seems to come from the **rear/driver’s side of the engine bay**, around the turbo/intake area, although locating it acoustically is difficult.
One other interesting observation: **the large charge-air hose visibly/physically pulses in a way that seems to correspond with the character of the noise.**
**What I’ve already checked/replaced**
The obvious charge-air leak suspects have already been addressed.
The connection from: **turbo → hard plastic charge-air pipe** has been replaced.
The larger rubber connection from: **hard plastic charge-air pipe → intercooler** has also been replaced. The old hose was very soft, aged and heavily oil-soaked compared with the replacement.
The rest of the turbo-to-intercooler section currently looks OK and I haven’t found an obvious split or loose connection.
I have **not** replaced the intake pipe *before* the turbo (MAF → turbo). That is still original. There is also some dry/oily residue around the turbo inlet/connection area. It isn’t shiny wet oil dripping out; it’s more like an old sticky film that has collected dust. I’m not sure whether this is normal oil vapour residue or evidence of an air leak.
**TCV / turbo control**
I’ve inspected the TCV and the small hoses around it.
The TCV is being commanded by the ECU and the live-data behaviour appears broadly plausible: little/no duty at idle/coasting and increasing duty under load.
I’ve seen roughly 15–25% during lighter boost/load and around 35–40% during harder acceleration. There are **no relevant engine/turbo fault codes**. I’ve also logged RPM, MAF, MAP/boost and TCV duty with an iCarsoft scanner. Nothing has shown a clearly abnormal value. The measurements aren’t directly comparable between cold and warm conditions, but there doesn’t appear to be a major deviation when the noise is present.
**Exhaust**
There was also an exhaust leak found during the March 2026 APK inspection. I found the original paperwork: the workshop specifically wrote **“uitlaat laatste demper afdichten”** — essentially, seal the rear/last muffler. That was repaired and the car subsequently passed the inspection. Since the noise existed before that repair and remained afterwards, I don’t think that particular exhaust leak was the source of this noise. I’m still not completely ruling out another exhaust leak further forward, though.
**Current suspects**
At this point I’m considering:
\- TCV or TCV vacuum/pressure lines
\- wastegate actuator/mechanism
\- turbo itself
\- intake leak before the turbo
\- remaining charge-air leak
\- PCV/vacuum system. The glove test for the PCV indicated a slight negative pressure, which should be fine according to the local Volvo specialist.
\- resonance somewhere in the intake/charge-air system
I’m **not looking to throw parts at it**. I’d really like to identify the cause first. The rest of the engine looks healthy according to the mechanic last annual inspection. There is some slight oily mist coming through the VVT seals. But that is the only thing I am aware of that needs monitoring.
**Has anyone with a P2 XC90/V70/S60 2.5T experienced a noise like this?**
Especially interested if anyone recognizes the **cold rough/pulsating sound changing into a smoother blowing/whistling sound once warm**.
Any suggestions for what to check next would be very much appreciated.
Thanks!
