On my LW3, I had a buzz that would match up with the attract lights blinking, listening closely, the buzz was only coming from the right speaker in the backbox.
I floated my sound board (w/ 2 sided foam tape) and the hum associated with the attract lights is GONE!!!!!
there is a quieter buzz that's coming from DMD usage but its completely tolerable compared to the buzz from before.
ALSO I had a BTTF that would make a nasty buzz noise constantly.To fix it, I put EVERY SINGLE mounting screw in on the motherboard, nice and tight. motherboard was missing 2 mounting screws, replacing them completely fixed the buzz.