I have restored a System 9 Space Shuttle and the flippers work perfectly, except the right flipper makes a noticeably loud hum/buzzing noise when the flipper is activated. Even my wife asked if she was going to get electrocuted when she heard it lol. Anyways, I checked voltages and EOS switches and everything is as it should be. Anyone know what could be causing this noise? It looks like the original coil. I'm ok leaving it as-is, I just don't want to risk damage to the driver transistor or CPU board if there is risk of something shorting out.

Coil gets just a little warm. If I hold the flipper down when the coil is activated and slowly let the flipper rise to it's full upper position then oddly enough, no buzzing.

Regarding coil stop, why could that be the problem?

Thanks for clarifying that! Makes sense.