I don't know of a "quiet" DC system but I built my own sound dampening housing and it cut down the sound by way more than 50%. In making the housing, I covered the inside and outside with carpet squares glued on with contact cement. I also wrapped carpet felt around the pipe - held on with electrical tape. Because I live in Japan and houses are CLOSE, I had no choice but to make an enclosed housing, and it worked.
As to the best for a small shop, I can't help with that. I am using a Japanese Makita portable DC unit that is not available outside of Japan.