I think the Rena airpumps are the quietest. I really couldn't even hear the one I used to have (now I have a filter that doesn't run by airpump) but when I had it I never heard it vibrate or buzz. It has little rubber feet and that must make a difference. You attach the rubber feet over the metal part. It's kind of a thick piece of rubber.
The other airpump I had was a Tetratec. It was very powerful and I used it to drive two sponge filters in two different tanks. I don't know if the similarly-sized Rena could have driven two sponge filters. But the Tetratec was loud and it drove me crazy almost every day. It always gave off a low buzz and then it would start vibrating rather loudly. It did have rubber feet too, but they were small and flat - not a lot of cushioning between it and the table. I tried to put it on something to cushion it but with no luck. If the cord touched the wall, that would even cause it to vibrate horribly.
For your bedroom, I'd definitely get a Rena.