Mine vibrates the bed somewhat, and I can hear it running, but it's not that bad for me. I was able to sleep with it running, which is pretty impressive - that sort of thing would usually keep me awake.
Now, mine is a new one (replaced last year); it's possible it's a bit better than the original one. However, I didn't notice a huge difference in how the two of them ran.
But you're not the first to mention this, someone on the Yahoogroups (which is now replaced by the B190.com site mentioned in my sig) mentioned it a while back, too. I'm sure some people are just more sensitive to it, and I'm afraid I really don't know what to suggest to improve the situation - there's really not a lot you can do with the mounting or anything.
Verify that the generator exhaust isn't leaking and isn't loose. That'd be an easy one to check.
1995 Airstream Classic 30' Excella 1000
2014 Ram 2500 Crew Cab with Cummins 6.7L Diesel
Sold but not forgotten: 1991 Airstream B190
Sold: 2006 F-250 6.0L Powerstroke Supercab