Quoted from Crash:Someone just posted this, claims a new DMD solved his problem. But it's a Williams game, not Data East.
http://pinside.com/pinball/forum/topic/audio-feedback-hum-went-away-after-installing-nos-dmd-wcs94-wpc
That would be an easy check, turn on machine, listen to hum, unplug Power to the DMD. Either the hum goes away or not. You get an immediate answer.