My auto shut off began to not work. It came on gradually, at first, just once in a while it would not shut off, then it got more and more frequent. Now it almost never shuts off and I have to reach over and shut it off manually. Also, I noticed the air turbine sound has been fluctuating. As a test, I removed the hose completely at the back, and then it did auto shutoff after a little while. Something must be going on with the pressure sensing. My machine is about 4 years old. I've used it every night with one or two nights when I didn't have it with me, but otherwise I use it religiously, even when I take naps which I do a lot because of chronic fatigue and autoimmune issues. I'm wondering how long these last typically. Maybe I'm due for a new machine thought I can't afford one right now any way. Any info is appreciated.