Today’s machines are whisper-quiet, so excessive noise may indicate a problem. Start by checking the machine filters. Disposable filters should be changed twice a month or when visibly discolored to help keep the machine running smoothly.
If the PAP machine has a humidifier, you might hear a slight noise when the machine cycles air over the water.
There may be a slight audible noise if you are using a BiPAP machine, which is the result of the pressure transitions between inhalation and exhalation settings. There may also be a slight noise when an APAP machine changes inhalation pressure.
If your machine is otherwise excessively noisy, there may be a machine defect.