cav551:
A Rotary compressor is quieter than a piston one but the ones I have had the misfortune to have to work near have been extremely aggravating and tiring. Maybe it was because someone else was making the noise rather than me. I think it is the pitch of the frequency which eventually becomes so wearing after an hour or so. In the end I found it so distracting that I had to limit what I was doing to tasks which were not particularly mentally challenging, until the thing had been switched off. All have been large cabinet units with very large reservoirs running either a production process or another application with a high demand, but they just never shut up they ran continuously, unlike a piston one which cuts out these just keep going.
Our two are outside and between the workshop and the compressors is the enclosed steam clean bay and you can still hear them, to be fair not all the time and its not that intrusive, but the noise outside!