[Porchdog]

I have used isolation feet under the compressor which helps. The big improvement I have made is to fab up a hose adapter and use radiator hose (and tube if it is a long run) to pipe the air inlet outside and put a protected air filter outside. That move most of the noise outdoors, which may not thrill your neighbors.
With the popularity of "cold air intakes" I have seen custom intake "kits" at the auto parts store, which might be easier than my solution with radiator hose.

You can also use compressed air or nitrogen in bottles for your dry system but there are some code requirements for monitoring pressure.