content: This arrived a couple of days ago, and I ran it at the high setting for an hour as directed. Then I moved it to the low setting. An hour or two later the machine started to make a high pitched noise, like someone holding one note on a clarinet or something.I tried turning it off for awhile, running it at other speeds, no help. The new noise is actually at all three speeds, it is just very apparent on the low speed because the higher speeds produce so much white noise that they almost drown it out.Has anyone else experienced this and know of a fix? I hate to ship back this heavy item, plus I had hopes it would help with a problem from my neighbors using an outdoor firepit a lot, which raises heck with my lung condition.