Quoted from ROMM:Sheeesh that’s crazy you are still having the issue after all the fixes and upgrades you’ve done. My machine sometimes does nearly the same thing as you described, however, it will have all sound, but no music. But when the next ball starts, the music starts. It doesn’t do this often, and it is usually immediately after powering up the machine and starting the initial game.
You are pushing the start button before the sound board has booted and gives it 'bong' tone.