I only have the base model. I don't have any of the C-Flex or auto settings. I've put pads under it, checked the filter, and have it below bed level. I just played around with it some more. When exhaling normally, the blower or motor inside the unit whines. During the night when everything else is q...

I recently acquired the basic M-Series model, and I don't like the noise it makes. The normal running noise isn't too bad, and I could deal with that if that was all it made. But I noticed from the outset that when exhaling, the machine makes a distinct low/mid frequency moaning/whining/humming nois...