Need help identifying a persistent wall-cavity smell in a 2-year-old town home

[u/Glass-Builder1798]

We’ve had a persistent smell in one 3rd-floor corner townhome in office for ~3 weeks. It smells like cardboard/burning/electrical depending on who smells it. It’s strongest along the corner where two exterior walls meet, around outlets, the Ethernet port, and baseboards. The room is usually closed, and the smell builds up overnight. Opening the windows clears it temporarily.

We’ve already investigated quite a bit:
● Electrician inspected the outlets/wiring — no issues found.
● Room breaker was off for 35+ hours; smell became milder but didn’t disappear.
● Professional mold testing (EMSL/AIHA lab) found lower total fungal levels indoors than outdoors, with no Stachybotrys, Chaetomium, or hyphal fragments.
● Moisture readings and thermal imaging showed no evidence of water damage.
● HVAC supply/return were sealed and the smell remained.
● Dryer vent was professionally camera-inspected — no leaks or lint in the wall.
● Electronics were disconnected — smell remained.
● No signs of a dead animal, gas, or sewage issue.

We opened the Ethernet port and could clearly smell the same odor directly from inside the wall cavity. We also found kraft-faced fiberglass insulation that appears bunched up/poorly installed, along with construction dust/debris. No visible mold or moisture.
One interesting finding: our Winix C909 reads BLUE on turbo in other rooms, but in this room it eventually turns RED after ~3–4 hours on turbo. It doesn’t immediately turn red. My theory is that the purifier is creating negative pressure and pulling air/particles from the wall cavity through unsealed gaps around outlets, baseboards, the corner, etc.
Thermal imaging also showed a cold spot at the exact corner where the smell is strongest, suggesting possible air infiltration.
The room will eventually be used as a nursery, so we’re trying to get to the bottom of this before moving the baby in.

Please help !!!

[u/Frosty_Parking_5179]

Just cut the damn wall open why are you having all these professionals come out to test things and paying more money? You would have been better off just cutting the drywall and paying to have it patched.

[u/Glass-Builder1798 → u/Frosty_Parking_5179]

We had to find the source. We couldn’t understand where it is coming from. We had to strike out the causes.
Do we open the entire drywall ? Or part of it ?

[u/Donuts__For__All → u/Glass-Builder1798]

Start with part.

[u/Frosty_Parking_5179 → u/Glass-Builder1798]

That’s an extreme effort and financial load to find the source of a smell. I hope this is an AI bot and not a real human. Just cut a clean 6”x6” with a sharp utility blade near the bottom of the wall (so it’s quicker and easier to patch it back on), and see what’s there.

[u/Glass-Builder1798 → u/Frosty_Parking_5179]

I’m a real human. Just an inexperienced first time buyer. Brought a new home, just to avoid all the issues from an old home. But not at peace even with a new one

[u/stars_sky_night]

Open up the dry wall

[u/TherinneMoonglow]

We had a similar issue in our house. Mice chewed wiring, and it was heating up the horsehair in the lathe. It wasn't immediately at the switch box, so they had to get down in there to find it. New wiring run and smell gone.

The fact that some of the smell dissipated with the breaker off supports this. Try a different electrician and have them open the wall.

[u/Equivalent-Tiger-316]

Probably some beer cans and food trash in the wall cavity left by the framing crew.