I've been working on a comet, finished up with the whole thing and everything was playing well for two weeks. Now I've got a loss of background sound and the occasional game where the sounds aren't correct or are missing. Any ideas where to start troubleshooting?

I found that for whatever reason the NVRAM that was installed keeps corrupting. If you do a factory reset, it fixes everything, but if the game sits for for longer than 24 hours, it corrupts again. Anything shorter and it's typically fine (though not always)Highscores get messed up, the number of balls, music and sounds, ect. I've swapped 3 different RAMS, all from the same batch and they have the same issue. Any ideas whether it could be the ram or something on the board causing the issue?