My BF obtained his machine/mask last week and is already noticing a difference. His machine is very quiet and I found the noise it emitted to be rather soothing. I did tell him this morning he sounded like a distant tea pot that was ready for his mask was emitting a gentle whistle throughout the night, seems his mask was leaking. My kittens, Twister and Penelope, were quite intrigued by the machine and mask and took turns throughout the night inspecting it from various angles.