My Kenmore gas dryer develops a progressively louder hum/buzz as the dryer heats up. If it runs long enough, a squealing noise is also produced. It makes no noise if started in "air fluff" mode with no heat. I replaced the rear drum bearing and inspected the belt and idler arm for wear (they both looked good), but the symptoms persist.
My guess is that it could be the motor, but it seems odd that it would only be affected when the dryer is making heat.
Thoughts??
-atetra