Hi, hoping someone could help me with this. When I turn my AC on upstairs (3 level house), I hear a low to moderate rattling noise upstairs. When I checked out the furnace room in the basement, I could also hear a similar rattling noise in the ceiling where the vents are. There's no noise from the actual AC units outside.

Thanks.

Is the noise coming from the furnace?

Hi, the noise dose not appear to be coming from the furnace- just checked.

Any changes to your heating or AC layout (vents, other equipment) prior to this noise?
When did this noise first become evident to you? Just a shot in the dark, but it sounds like vibration in the ductwork in general. H
Ave the ducts been cleaned in the last few years?
Is your filter dirty?
Obstruction in the supply ducting might create higher static pressure when the fan kicks into high speed.
Rattling in the furnace would have introduced the possibility that the blower was causing the vibration, but you have apparently ruled that out already.