But are they quiet, quiet, quiet? The difficult question to answer,
even if you have noise level specs for fans, is how much of a
difference will I notice when compared to my just plain off-the-shelf
parts computer?
Yes - my DAWs are quieter than the average off-the-shelf computer.
Obviously, this would depend on the computer because some are louder
than others.

My DAWs are not as quiet as machines with no fans at all but these
computers are pretty expensive. However, the fans in my DAWs are as
quiet as they can be.

Unfortunately, I don't have audio level ratings for my machines.
There was a recent article in PcWorld on silent PCs - it may be
online.

Mike