I'm sorry- I went all through the manual, the spec sheet, and Quincy's site and I don't see where Quincy has posted a decibel rating for this unit.
There isn't an industry standard (so far) for dBA ratings- so readings could be taken 3 feet away or 10 feet away; in a noisy room or a quiet one. This lack of consistency is one of the reasons many manufacturers won't post a decibel rating.
However- my experience with Quincy piston units is that they are quieter than many others on the market, thanks to quality components and low RPM pumps.
You can see compressors that are built to be quieter than normal in our
Quiet Air Compressor listing.