I'm finishing up a playfield swap on a Gottlieb Waterworld. The game is 100% now except for speaker hum coming out of the bottom of the cabinet. I don't have a lot of experience with Gottliebs so I could use some help. I can't imagine this is normal. I've reseated all the connectors and changed the two big caps on the sound board. I'm not seeing anything else that looks like a problem but the hum is very annoying. Thanks in advance for any help you can offer.