Hi; One year ago I installed a Fantech FG4 inline fan in a return-air system that brings cool air back to my stove room. I got some good advice here on controllers, and it worked well. But, when I started it up again this fall, it was suddenly noisy, with a grinding/whine noise that was not present last year. Any ideas what is going on? Could the fan have gotten dirty, or become imbalanced? There is a high-pitched grinding whine, that oscillates a bit.