Charlie, I've been out in the country and away from people and big stores for so long that I've forgotten what Celotex is. I was thinking that it was the black builders board. I believe that they have a slight odor to them. Anyway, any foam board would work to deaden the noise. You're right about the noise. You need to know if it is the compressor making it. The blanket won't help if it's the fan making the noise. A service tech should be able to tell you. I could tell you how to determine which it is if your neighbor would give you permission but I don't know how handy your are around electricity so I hesitate to do that. If it is the compressor, a blanket will help. Another way where you don't have to buy the blanket is that you can use fiberglass insulation and wrap it around the compressor. If the noise lessens then it's the compressor. Good luck, that's part of the reason I'm in the country.