We use our microwave to make bacon for breakfast, the microwaveable cooker is so large that our microwave’s turntable cannot rotate, so after a while our microwave starting making bumping sounds when we used it. I found your page here while searching for possible reasons online! I did what people here had suggested, I checked for flat on spot/s roller wheel/s, found none, I wiped all the roller wheels clean, and also cleaned the track that the rollers wheel travel on the microwave. Thrilled to report, no more bumping sounds, our West Bend Microwave is working like a charm!