"Hi Ho Silver" wrote in message
link.net...
The rush of return air flow through my plenum cover and air filter is very
noisy and I am wondering if the builder left out some noise reduction
feature. This is not 'mechanical' noise, but the 'wind rush' noise.
The return filter opening is at floor level and the air makes an
upward turn to enter the fan suction which is about 30-33 inches
above the floor inside the return plenum. The filter size is 20"x25".
The
actual entrance to the fan is smaller, looks to be about 18"x18" (perhaps
that hole is too small?). There is nothing between the filter and the fan
suction; should there be some kind of 'noise reduction baffle' in that
location? Any hints appreciated. Thanks,

Sounds to me (O.K., I can't hear it, but you know what I mean) like the
ductwork was not sized properly. If the system has been "choked" down
(improper return size or not enough supply vents) then you can get all kinds
of noises.....