iNAP is very quiet by design when the pump is running, and doesn't emit any sound when the patient reaches the set pressure (seal condition) as the pump is idle.

When we ship iNAP to new patients, it is set at the lowest pressure and intensity setting. As some patients need a higher intensity setting, they will hear a slight increase in noise from the pump as it spins faster and works harder to reach the target pressure faster. A higher target pressure setting will also act in the same way and increase the noise level. While still very quiet compared to a CPAP machine, the noise from the iNAP console may disturb the patient or bed partner while they sleep. 

The silencer is an extra layer of material covering the bottom of the console where the pump is and significantly dampen the amount of noise produced. It is a simple and inexpensive addition to iNAP to improve patients comfort and experience.

You can purchase silencers here.