Just like the average CPAP machine, the CPAP cleaning devices started noisy and have gotten quieter with each upgrade that they make on them. Each different model has a different level of noise associated with them. The units that utilize ozone have a soft humming sound to them while the UV light CPAP Cleaners only admit a beeping noise to indicate the changes in the cleaning cycle.
CPAP cleaning devices are generally much quieter than the CPAP devices that they are cleaning. Most people who utilize these cleaners use them on an automated cycle or set them and do something else and do not typically feel disturbed by the noise or sounds that they emit.