Heating, Air Conditioning, Fridge, HVAC/Intermittent air return trouble

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Question
I've been in my house nearly six years, and for the first time we're suddenly getting loud vibrating sounds coming from our air return. It's not constant. It first started several weeks ago, lasted a couple of weeks, and then disappeared. Suddenly again today it's returned. I've been reading that this sometimes happens when there's insufficient room for air flow, gaps around filters, and overly restrictive grilles. But I can't figure why it might suddenly start happening now, out of the blue.

If I take the grille and filter off, it goes away. When I put them back on, the noise returns instantly. I've tried using weather stripping to close the small gap around the filter. I've tried different filters, too. Nothing I do seems to make a difference. The sound just seems to stop on its own.

Are there other factors that can cause this? Can cold temperatures outside make a difference? I can't think of why they would, but I've noticed it seems to happen most on really cold days. The HVAC unit is outside, and it's been an usually cold winter.

We had the unit cleaned and tuned up in the fall. Also in the fall I caulked up cracks in the return vent. I can't think of anything else that's different. It makes the sound all the more annoying that I can't seem to do anything about it.

I'd be grateful for any suggestions.

Answer
Normally just removing the filter and not the entire grille will stop the noise.  I know you have been there for a few years, but that does not make things right.  It is possible if the fan runs at different speeds, when it goes in to high speed the grille is not quite big enough and the velocity of the air is greater then what it should be.  There are other variables that could come into play, but without first hand knowledge there is not much I can really do for you.

Craig  

Heating, Air Conditioning, Fridge, HVAC

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Craig HVAC Expert

Expertise

I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.

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I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

Education/Credentials
5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

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