I'm renting a 1 bedroom condo in a 4 year old building, which has a central AC/heating HRV system (it's a 4-pipe vertical stack fan coil if that means anything). Picture below.
I've discovered the motor/fan for the 2 exhaust vents extracting air (one in the bathroom and the other in the main living room/kitchen area) makes a loud mechanical sound that carries through the vents, sounding like a high-pitched whistle/whine. It's hard for me to ignore because it changes in volume, louder to softer continuously on a loop. I've measured it at 56 dB with my phone app.
The blower motor/fan for the heating/cooling portion is quiet, as is the main return duct for the fan coil, it's only the other fan that is loud and echoes.
Landlord arranged an HVAC tech come out to look at it, he turned down the fan speed which didn't do much, and said it was all he could do (he didn't attempt get into the fan itself or inspect the ducts).
I am a renter, so getting into the drywall or re-configuring the ducts is not an option. While I can turn the exhaust fan off since it's separate from the heating/cooling, that's also not an option because of moisture/mold/CO2 accumulating.
I found this answer to a similar question suggesting to line the portion of the duct I can reach into with a material to dampen the noise, but that was specific to a vent that is supplying heat/air, while my noisey vents are intaking air. Can I still try this out without it being a hazard? (lining inside of the duct near the vent)
Otherwise I've tried headphones and a white noise machine but I'm hoping there is something I can do to reduce the source of the sound at least a little, please help!
