I have a new condo unit located on the top floor of my building, but the noise from the AHU on the roof can be clearly heard through my bathroom's toilet exhaust fan. Basically, it sounds like the exhaust fan is always on even though it's off.

Are there any ways I can reduce this noise from my own unit with the least amount of meddling with the entire system (since I don't have access to the HVAC system)? Are there any foam products I can insert into the duct that still allows air to flow through but reduce the noise, or a specific exhaust fan model that I can replace in my unit that addresses this issue?

Any suggestions are greatly appreciated.