Help: HVAC air return grille “sings”

[Alkali Ike]

Any HVAC experts here?

The 24" x 16" steel air return grille on my HVAC system makes a high-pitched tuning fork kind of noise. I've always tried to ignore it but it's getting really annoying. It's absolutely 100% the grille, not the system.

Googling suggests it could be insufficient return airflow. Too much air passing through the grille, implying the return is undersized.

I've played around with blower speed settings but the grille sings even when the blower is on "low" (I've returned it to the original "medium" setting).

I haven't been able to find a 24 x 16 replacement online that isn't pretty much the same design and made of similar stamped steel.

Anyone have any DIY suggestions? Or do I need to bring in a pro?

Edit: The entire grille resonates with the noise. I removed the grille and it makes the same noise when I tap on it with a screwdriver handle.

 

[Matt Liebenau]

I was an HVAC service tech for about 8 years. I don't know about where you are but where I lived at the time very few houses had adequate return ductwork.

Having said that, I did fix many "whistling" return grills by taking needle nose pliers and bending the individual fins a bit. Typically so they were more in line with the air flow and blocking the grill less if that makes sense. You might have to play around a bit with which direction and how much to bend. Also the (typically white) finish on some of those can be easy to scratch so you might end up with some paint scratched off. Sometimes it also helped to remove the grill part and bend or tweak it a little in order to try and stiffen the whole grill up and keep it from vibrating. Usually bending the fine did the most good.

 

[Matt Liebenau]

At about 10:00 in aged does what I was talking about.

 

[Al T.]

I just fixed that problem, I replaced a 30 day old filter with a new one. The filter had bowed and was letting air flow between the filter edge and the frame of the return air box. Undersized returns seem to be a common problem also.

 

[Alkali Ike]

I just fixed that problem, I replaced a 30 day old filter with a new one. The filter had bowed and was letting air flow between the filter edge and the frame of the return air box. Undersized returns seem to be a common problem also.

The filter on my system is at the furnace end, nothing behind the grille except ducting.

I'm going to try straightening out all the louvers in the grille. I've worked out how to do it without scraping off paint and getting each one flat at more or less 90 degrees with the grille instead of the original 45 degrees. The bad news is there are 4 columns of 50 louvers, so 200 of them to do. It's a little tedious but I'll get it done.

 

[Jeff Scott]

When we had a HVAC system installed in the attic we had the same issue; it was those cheap, flimsy big box registers. I got much better and much nicer looking grills from Pacific Register (there are other similar companies out there, too to check out).

Decorative Register And Vent Covers | Custom Vents

This is the air return register; the output side of the system has directional louvers behind them.

 

[Pilgrim]

It's just the grille interacting with the flow rate of the air. If changing the flow rate doesn't correct it, modify the grille. You can tweak the fins as suggested above, or perhaps try threading a ribbon through the fins as a motion damper.

You can even change the grille if needed, or remove it when it drives you nuts. A return grille usually doesn't have air moving through it fast enough to cause this. Perhaps your building should have more air returns.