"DN B" wrote in message
...
The most likely place is close to the furnace in the return air
duct..especially in the middle of a long duct section. It is referred to
as :'Duct Boom' . Usually caused by thinner sheetmetal . Simply push on
the center of each long section of return air duct , near the furnace,
and duplicate the noise youre hearing. Then add a brace across the
entire section of that area and screw it on. This will hopefully stop
the duct from vibrating/being sucked in. If for some reason you cant
add a brace due to space limitations...then wedge something in there to
stop the noise. Good luck.


I had the same problem, and just wedged something against the duct so it
stayed pushed in.