we have been having this problem and was wondering if you find the same thing or even better a solution. After we Mod a hydro and install submersible pump units and rupture valve the noise level in the machine room and car is considerably louder than before the mod. We add isolation couplings and isolate all pipe supports. Keep as much oil in the tank as it will hold. We have tried air up mufflers and older standard mufflers and neither one seem to improve the situation. We have found the Thyssen rupture valve to be quieter than other models. We have taken to getting sound disable readings before and after to insure its not just people getting use to not hearing the elevator run. Also we have added x-tra isolation pads under the tank and under the pipe supports. Different suppliers of pump units don't seem to matter as they all seem to use the same motor pump combination. But maybe someone does a better job of isolating the unit? Anyone have a preferred unit because of this problem?