Electromechanical pinballs with AC flippers will normally have a perceptible
hum when held. If this is instead a loud buzz you may have a problem.
First check your coil stops. If they don't have an internal copper ring
visible they need to be replaced. You may also need to replace the plunger
or file the end so that it will firmly seat against the stop. You may have
a problem with the hold winding (the finer wire one) not coming on, or staying
on. Usually this problem is characterized as chattering, not just a
Secondly, check that your end-of-stroke switch is opening and closing
properly. If the EOS switch is not working it may cause this buzzing
and burn out your coil quickly.