My guess is it's still a watchdog circuit problem, even though it's doing it by itself and not by the usual "Double Flipper" trick. If the caps have got to the point that they have virtually dried out, so in other words, never been replaced before then that part of the circuit could be wavering on the trigger point all the time even without the two flippers being used at the same time. I say this because my Getaway did a similar thing a year or so after i bought it, did a few random resets at first and then became more evident when the flippers were used. As for the diagnostic leds, well that's got me thinking I've not seen that on any of my machines as yet. The static is most likely nothing i would guess, it doesn't take much for the speakers to register a bit of static noise and i don't think it's an indication of the issue you are experiencing. I'm looking forward to seeing what some of the more experienced pinheads have to say about the led thing though.

Have you seen this?

http://pinwiki.com/wiki/index.php?title=Williams_WPC#Game_resets

Oddly enough, my STTNG just started doing this the other night. It's had "double flipper" reset issues in the past, which went away when I re-seated connectors as a quick "fix". Even then, the game is fully LED'd and the LEDs would dim on a double flipper. Considering their nominal current draw, I knew I still had a problem.

NYE party, about 10PM we're all upstairs and I swear I hear "BONG" coming from the basement. I hear it two more times and go check it out, and sure enough, it's STTNG rebooting itself in attract mode.

The Wiki page above is the answer key. I just now need to methodically go through the steps to find the culprit. And I'd recommend the same to you.

this should resolve the HSII reset issue . . .

https://pinside.com/pinball/forum/topic/announcing-new-product-to-help-resolve-resets-in-wpc-era-games/page/7#post-2491500

Great product, My Getaway was doing something similar, put in a new power board, re- seated all connections and would still get resets after about 45 min of being on even in attract mode. Make sure your plugging the game directly into an outlet and not using a power strip. This product has taken care of the issue and it's been over 2 years without a reset playing the game daily.

I had the resetting issue, sometimes the dbl. flipper, sometimes multi-ball, random multi coil activation. Bought one of these all problems gone,

http://www.kahr.us/