I have the ResMed AirSense 10 Autoset too, and have been struggling with the noise also. No help from the DME. The loaner has the same issues. I've compared them to two PR machines that friends have, and those machine -are- quieter.
At present I have tried putting the machine on a towel, neoprene gym mats curved over the top of the machine (alsways leaving the intake vent free from obstruction), putting the machine on the floor below head level, and always wearing earplugs.
The machine will also develop a high pitched whistle sometimes. I've checked all the seals and they look ok. My best temporary solution has been to put a blanket over the whole desk top that I put my machine on, fold up a thermal blanket the kind with loose weaves, put the machine on top of the thermal blanket, put a tight woven small throw rug folded up several times on the top of the machine (leaving the vent free) and wrap a towel around the side with the hose connections - and wear earplugs.
I'm in the compliance period still. But, have contacted my insurance company to change DME's with the hope of getting a different machine. However, not sure if I will be allowed to change companies.
Everyone here has said that their machines are quiet, and today having heard a friends PR and how quiet it is, I'm hopeful that if I can change brands that it will be the solution.
What a shame. The S9 doesn't have this issue. I will see if I can exchange it for the S9.