Air Conditioning - Buzzing in the attic

I recently purchased a new townhome and have had a problem with the a/c cooling during the day as not enough air was coming out of the vents. After a couple of visits, the contractor finally replaced the plume in the attic, and the cooling problem was solved.

However, the past few days I've noticed a humming noise in the morning, which I finally traced to the a/c unit in the attic yesterday. The noise is constant, even when the air conditioning is not running. I couldn't detect anything that was loose and vibrating and when I press against the unit, the noise still continues.

The noise is not very loud and I don't even notice it with the tv and ceiling fan on. They replaced the plume a couple of weeks ago and I was out of town several days, so I'm not sure if the noise began then or not.

Any ideas of what's causing this or what can be done?

I'm not sure I can provide a solution, but I can identify the source of the sound... There is a transformer in the A/C unit that supplies low voltage to the thermostat and control relays of the system. It's on all the time and some seem to "hum" more than others. You might turn off the power and look inside to see if you can find a small metal box with 2 big wires and at least 2 small wires connected to it. Check to make sure it's tightly attached to it's mounting. If that doesn't help and it really bothers you, call an A/C technician and see if they can replace the transformer with one that doesn't hum as much. There isn't likely anything wrong and the new "plume" probably gave more room for the sound to travel in.

Doug M.

here are a couple of thoughts

if it is the transformer, i have heard that reversing the polarity on the supply voltage to it will cure this
i have not tried it myself, but heard it from a very credible source

if the "plume" is what we call a "plenum", it is very possible the installer has a loose piece of silver tape that air is escaping under, kind of like blowing on a piece of grass

rub down all exposed tape, if any, and listen to noise at the same time

Thanks for the information. I took off the outer casing last night and there was another metal plate inside that was a little loose. I tightened its screws and that muffled the sound somewhat; however the noice was noticeable again this morning. I'll try to tape it tighter, but if that does not work, how do you reverse the polarity of the supply voltage?

Aw the transformer. You have been there so you know you can put a rubber washer under it. Dont tighten the screws or just one. Bend up one layer of the top of it. change the power to it like hvac4u said it works some times
Are for the cost of it just go down and get a new transformer make sure the volt amps are as high as the one you have there now or better.

ED ;)