This unit worked great for 4 years. Installed it in the window for the 5th summer, and it didn't work. Just a low humming sound at first, then the fans eventually started going and they made a very different, much louder sound than usual. The fans moved freely without any blockage or obstruction, and no bad grinding sounds or anything like that, so I don't know what the issue is. [This review was collected as part of a promotion.]