I had a similar problem (buzzing switch motor). The anti-derailment feature of MTH switches uses the inside rail on both the straight and curved sections down from the frog as an electrical switch to detect a train when the switch is set the wrong way. The farthest most end of both those short rails that form a "V" in the switch need to NOT touch the adjacent track section rails. That is they should be electrically isolated. MTH makes those track too long and they can touch the adjacent rail and the switch thinks it is a train and tries to change the switch. I had to shorten the "V" section rails in each of my seven switches to get them to work correctly. When the wheel of the engine rolls across the gap in the rail, it completes the circuit to the switch motor and the switch changes to avoid a derailment. They work perfectly if those "V" rails are isolated.
Switch motors are only suppose to be energized momentarily. When they are continuously energized, as would be the case with the too long rails, the switch motors over heat and burn up. They buzz if there is a continuous voltage on them. They have been know to catch fire.
LDBennett
