Quoted from RyThom:
The music doesn't just cut out when you add service credits - it cuts out when you adjust the volume mid-game, too.
Sorry, but this is just bitching rather than a "bug".
It is not an intended purpose of the machine.
When playing the game, you should be playing the game, not trying to add service credits and adjust volume.
They have the music play during volume adjustment anyway, and if you have a key, put it on free play!!
I mean come on, you're clogging a bug thread with crap that is just not relevant.