Screw compressors are not really quiet. We have a half dozen of them at work and they are quite loud. They are made for high volume continuous duty, not really harry homeowner equipment.
I did a lot of shopping around and ended up getting a Quincy. Buy one of these and it will last your lifetime. The key to quiet is the low RPM (1750). I had mine in the garage for a year but it put out too much heat. I built a compressor building attached to the outside of my garage and its perfect. Its been out there for 2 years and its the best thing I ever did.
When im in the garage I can just barely hear the compressor running.
Quincy QT-7.5 Splash Lubricated Reciprocating Air Compressor with MAX Package 7.5 HP, 230 Volt, 1 Phase, 80 Gallon Vertical, Model# 271C80VCBM | Northern Tool + Equipment