Put it outside.
If I put it outside I will annoy the c#@% out of the whole block!
I am not living in a little house on a priory. Even in small villages here the houses are very close to each other.
I can always wear internal and external earplugs and keep it inside, but my concern is annoying my neighbors.
The best fix would be to shoot it and put it out or your misery.
I do not own any firearms and even if I did, it would be illegal to shoot it anyway. Besides, I am only allowed to own smooth-bore shotguns where I live and the shot will ricochet and end up on my face so it is probably not a good idea.
The Compressor is relatively new; made in 2009 and I used it like 2-3 dozen times so most parts can be salvaged.
You haven't given much info about the compressor?
Yes. Too bored to find the manual because modifying the compressor is actually "Plan B". If I decide that modifying it is the best course of action, I will go through the trouble of finding the manual.
I have an oil less HF compressor that's very loud also. Mine's under the bench so that helps keeps some of the noise down. You would have to allow for some ventilation, but that can be worked out. Just locate the baffles in front of the vents and foam line the interior, keeping it away from any heat sources.
As far a refrigeration compressors they are completely different these days. My very first home built was from a refrigeration compressor, but that was 40 some years ago. It was from a 2 stage piston type and that worked OK, but I upgraded it as soon as I could afford it. My large 5 HP is also oil less and it makes a racket that you can hear from inside the house and the shop is 2 walls apart....
Yes, heat is an issue in the Summer, but usually the compressor will have to fill the tank a couple times; which make it already too hot.
What you describe seems to be vibration and/or low frequency noise. This is an issue for me because you cannot really do much about them.
It is like if your neighbors have a party and you cannot hear the music but you can "hear", or more precisely, feel the beat of the Sub-Woofer.
The house where I live happens to have an old American style A/C. The square thing that goes completely through the wall. The owners think about removing it so I can ask them if I can have it or even buy it from them if they remove it.
I may also be able to find a refrigerator that is 20-10 years old. Or maybe even 30, but 40, no, probably not.
By the way, I can most probably only get my hands on EU refrigerators. These comply with EU laws and guidelines and operate with 240V 50Hz power so they might be different than US refrigerators.
I would not mind going with an option like making it Foot Powered via pedal. I do not use it for painting anything large or use it too often and it would also be a good opportunity for a workout.
But playing with things that can kill without knowing what I am doing is not logical, so I sit down and do "asking and researching".