This quote is hidden because you are ignoring this member. Show QuoteThat was my issue with a couple air return ducts closest to the furnace.This quote is hidden because you are ignoring this member. Show Quote
For years they sounded like a turbine engine and I thought it was "normal" until one day I made contact with the grill and the noise went away.
I've just place a magnet strip on the back side of the grill to stop the vibration and it fixed the issue.