Start by reflowing the solder to the headers pins on the sound board and driver board. Probably best if you reflow the header pins on all board in games of this era. Better yet, replace all the header pins with new but that is not a casual undertaking.
If that does not fix it, suspect the ROM and/or CPU chips on the sound board (not the voice board). Reseat the ROMs or beter yet carefully clean the pins of the ROM with a fiberglass sanding pen, or even better than that, replace the ROM and CPU sockets with modern dual-swipe type.
Newcastle, OK
