I have a ResMed S9 AutoSet machine that is currently programmed to run in traditional CPAP mode. It is connected to the heated humidifier and ClimateLine (heated) tubing from the machine to the nasal mask. The machine is very quiet. With a good mask seal, the noise from the machine is barely audible. The only noise that I notice is a slight high pitched whistling sound that is in synch with my breathing. I assume that is from the air passing through the humidifier or the tubing. The sound was a little annoying at first, but I've gotten used to it.
My wife doesn't even notice the noise from the machine. I think she sleeps better now that she doesn't have to listen to my snoring
My only complaint with the S9 machine is the modem that was supplied with it. The machine is supposed to send data to a special secure website that my doctor can access to see how well the CPAP therapy is working. However, the cellular modem doesn't seem to work in my apartment. Could be a poor cellular phone signal problem. There is a data card that can be removed from the machine and sent to the doctor in this case.
For anyone using an oxygen concentrator, you can ask your healthcare provider about putting the concentrator in another room. I work in healthcare and I've seen that many people use 20 to 30 feet of oxygen tubing between themeselves and the oxygen concentrator. Unfortunately, the cpap/bipap tubing can not be extended nearly as far. However, it may be possible to add an extra 6 feet or so to the tubing between you and the cpap/bipap machine depending on your setup. (I don't think you can extend the heated ClimateLine tubing, though. Putting more distance between you and the machines should make things a bit quieter.