Some people report that the Z1™ is noisier than their bedside CPAP. This is due to hearing 2 different noises due to the size of the motor. 

The first noise is described as a wind or whistling noise in their mask. The air is circulating up from a small motor through a narrow tube to the mask causing it to swirl. This is more noticeable with certain types of masks. To reduce this noise, start with a longer standard hose and insert the HME close to the mask. If this is not enough, add the Qtube in line muffler (available online or from your equipment supplier). This is added closest to the CPAP machine and straightens out the path of the air to reduce the wind noise.

The second noise that people describe is a motor chirping noise from the small motor slowing down and speeding up with inhalation and exhalation of breath.  

The Z2™ averages 29% less noise at air intake than the original Z1™

Attached is a picture showing all of the assembled parts.