The discharge side does make some noise but very little compared to the intake pump. The discharge pump is a centrifical pump which are inherently quiet.
Our freshwater Quiet Flush is quiet... compared to the POP! of a VacuFlush at oh-dark-thirty... but I wouldn't say its better than sliced bread. Helps a bit to have the toilet lid down... doesn't hurt to have the door closed.
But also, as they wear, they get noisier. Our first pump eventually got much louder, and then started leaking a bit. The rebuild fixed the leak, but didn't fix the noise.
New pump fixed the noise. Back to my first comments, above.
FWIW, I suspect "quiet" is in the ear of the beholder. Modulated (a useful sound term) by whatever the beholder is used to, or comparing against.
I replaced a noisy head with a Jabsco Quiet Flush and it makes ten times the noise of the one I replaced. The noise is from the discharge pump, the sea water pump is so quiet you almost can't hear it. ...
The first discharge pump was so out of balance it just about pulled the toilet off the mounts. They replaced it but is still super loud. I even mounted it with rubber washers above and below the bolts. A real piece of junk. I don't know how they get off calling it "Quiet Flush".
Freshwater version? Hard to imagine where you put additional rubber washers? The motor attaches with four bolts pressing the seal housing -- and a small gauge/large diameter O-ring in the seal housing -- against the base assembly so it fits flush... Washers in between would disconnect that seal...?
Unless you're talking about washers on the bolts that hold the bowl to the base assembly, and/or the bolts that hold the base assembly to the boat?
Is it common for the motor lip seal to go bad in a couple years? I've replaced mine once and it looks like it needs replacing again. It leaks even when not in operation.
When I rebuilt ours that first time, it did begin leaking again not too long afterwards. Although much of that might have been because it was not an expert rebuild. Still, I talked to Paul at Jabsco at the time, also mentioning the "it didn't get any quieter" issue, and he suggested there comes a time when "you've gotten your money's worth" from one of those pumps.
I think that was when that first pump was about 10 years old, something like that. New pump, no leak, quieter.
-Chris