A quiet compressor?

Upgrade to a larger capacity, 2 stage (more efficient) compressor. Remember that an internal combustion engine is just an air pump powered by a fuel. You can build a big inch low, rpm stroker or a short stroke, high rpm motor. I use an 80 gallon, 7 hp, 2 stage compressor at home. I use it to supply my sand/bead blast booth. I wore out 2 60 gallon Craftsman oil-less compressors in less than 4 years. My 80 gallon 175 psi is over 11 years old now. The 60 gallon ran continiously and the larger model now runs from time to time. The more reserve capacity that you have, the less it has to work. Rubber mount to a concrete floor and install a large, free flow muffler. Just like on your car. More economical in the long run.