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Discussion Starter · #1 ·
I'm hoping somebody out there has had experience with this problem. I have an air intake vent that is located about 8 feet above my head on an adjacent wall.........and of all places in an obnoxious accoustically resonating corner. The vent inlet is about 24 in x 24 in square. Behind the filter, I can clearly hear that the sound is eminating from upstairs in the attic from the a/c unit itself. The noise can best be described as a moderately high pitched buzzing noise and because of where the sound is eminating, fills the room with a distracting unpleasant noise that I can no longer live with when listening to music or movies. Short of covering the vent with some kind of home built sound deadening panel cover ( which I imagine others would shy away from due to obscuring the actual vent from air coming in, are there any other recomendations to fix this problem. The only way to fix the problem is to go upstairs and turn off the a/c unit, which shuts the unit off and thus eliminates the irritating noise. Any help would be appreciated.
 

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I would take a look around up in the attic while the A/C is running. A buzzing sound sounds like something is loose and vibrating. If you can find the offending vibration, you may be able to dampen it at the source.


Short of that, you might try some acoustical treatments and the walls at the corner where this vent is located, to reduce the resonance and absorb any reflections.


Based on your description, it sounds like the air return goes into an attic plenum. You might be able to install some acoustical baffles in the plenum between the vent and the a/c unit, or line the plenum with acoustical treatments. These treatments would probably have to be fire rated (for building code conformance) so I would check with an HVAC professional before doing anything like that.
 

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Discussion Starter · #3 ·
cgblack, you are right about one thing. It is coming from the a/c unit. But it's not anything physically loose on the unit that is causing the buzzing. This is a high pitch buzzing noise that is coming from the unit while in operation. I don't know if this particular type of a/c unit makes this sound while in normal operation or not, but it's almost like an "electrical buzz" you would hear while standing underneath power lines...........and that is the BEST way I can describe the noise. Any other ideas?
 

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Durwood,

I think it is time to call your favorite service company and have them take a look at your system. DO NOT cover your return air grill or attempt to modify the ducts, you could end up doing more harm than good.


If it were me I would start by checking the amp draw on the indoor blower motor and add a few drops of oil to the motor if it has oil ports, not all motors do. Any chance the blower wheel is touching the housing when the motor gets up to speed? Is the noise constant or does it seem to increase as the motor gets up to normal speed?


I would also check for loose fitting doors on the air handler it self.


If you can get the model and serial number of the air handler I'll do a little research and let you know if there is anything else you should look at.


BTW I'm in the HVAC Biz
 

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My new theatre (new home delivery in July) will have the main air return on a wall near the front of the room. It will be on the left side of the room, opposite a sliding glass door that will be covered with black out curtains. I was considering putting similar curtains on the wall with the air return, for accoustic symmetry, but I don't know how to do so without blocking the air return too much. Any thoughts?
 

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Scott,

Blocking the Return ducts is never a good idea from an hvac standpoint. Doing so will cause your return air flow to be retricted which will affect the entire system. In order for a system to function properly it needs to breath, just like you and I. Your best bet would be to relocate the return air grill, possibly to the ceiling if your HT is going to be in a basement.
 
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