Just a quick follow-up. I took some db measurements as a baseline. With both units operating (not including startup), here are the values:

Inside bedroom on shared wall: 68 avg, 72 peak
Inside bedroom on opp wall: 60 avg, 64 peak
Outside between units: 84 avg, 93 peak

Yes, that's 93 db, no joke. On startup it's even louder, but haven't taken that measurement. Talked to the guys at Green Glue and may do alternating layers of GG and 5/8" drywall, twice on that inside wall. Add a lot of mass, we'll see how much difference it makes.

Here is a link that might be useful:

seems to me that if the units were not surrounded by hard surfaces that they would be quiter.for me that would be a better option..
best of luck

I do wish I could fix the location or surroundings, but that's the property line. Not the best of designs, I'll grant. We just moved in last month so I'm attempting to help the situation as much as possible.

First off has anybody checked the units to see why they generate so much noise? Even the bottom of the line units back then didn't go much higher than 80-82 dbs. Compressor blanket might help some but don't think it's the solution.

I don't think you'll get the degree of satisfaction your looking for with green glue or quietrock solution. Additionally, if there's a window in the vicinity it will continue to transmit the same level of sound through it as before.

If indeed the units are checked out and found to be operating more or less as normally expected, based on the age of the units and your inability to move them somewhere else the only real solution is to purchase new quiet units.

Or use some vibration absorbers under the units and some noise blankets on the compressors. It also sounds like they maybe oversized. Or4 maybe another malfunction.

Thanks for the responses. I installed one sound blanket on the 3 ton unit and it has reduced the vibration and the higher pitched frequency on that unit. I will measure the difference. I've ordered another Brinmar blanket to do the same with the other.

I looked over the units when we added the blanket and there are several screws missing and some parts that don't look to be well secured so that'll be my next bit. Also, looks like some weatherstripping was added for vibration just under the top that's rotted away. I'll replace when I add the blanket. Still considering the GG + drywall option as the final piece.

One more update. I've now installed compressor blankets on both units, added rubber weatherstripping to reduce vibration and tightened up any loose fittings. The 3T unit is very quiet now, only hear the fan motor for the most part. The 3.5T unit is tempered a little, but the vibration and volume indoors has not abated much at all. I've done a frequency sweep before and after and it appears as though 100-250 Hz are the highest volume culprits, topping 80 db indoors. The wall appears unable to attenuate those frequencies when you compare the indoor and outdoor measurements.

Did you put vibration absorbers under the condensers?

I don't know much about vibration absorbers. The units are secured to a concrete pad. On there securely as far as I can tell. What should I look for?