Just noticed this thread.

I do t know for sure but my guess would be to replace the capacitors on the sound board. If they are getting flaky then it could cause issues once the game warmed up.

Another problem might be a poor solder joint that is expanding once it gets warm, try reflowing any questionable solder joints.

I doubt that the problem would be a chip on the sound board. It shouldn’t be to difficult it shotgun repair any parts that look faulty.