I just took an old dish towel, folded it in half and put it under my old, noisy machine and it cut way down on the noise. My new machine doesn't make any noise that I am aware of, but then I never moved the old dishtowel I have under it!
As always, YMMV! You do not have to agree or disagree, I am not a professional so my mental meanderings are simply recollections of things from my own life.
PRS1 - Auto - A-Flex x2 - 12.50 - 20 - Humid x2 - Swift FX
Having a towel or absorbant pad underneath the machine is a good idea. Not only does it reduce the noise, but in case of a water spill or moisture leak from a hole in the hose, it is their to soak that up. My wife insisted on it soon after getting my machine. I complained that it wasn't necessary, but when it fixed the noise issue, I had to admit the wife knows best.
I'm having the same issue. It's been going on for quite a while and does get louder during the night. So much in fact I have to turn it off and try to sleep without it. Can't afford a new machine