sound issues

[emjeeman]

Sorry, let's keep this more on-topic. I've edited my first post and thread title to update the situation and to reduce confusion. The cheats menu problem has been solved and I only have the sound issue. To restate the issue:

I'm experiencing some real slowdown in the sound and it sounds jerky/static-ish/stuttering. The game runs at fine speed and video looks great. It's just the primary sound is slow and poor quality. Audio that requires Atrac3+ works fine, though. If it may be the cause, I'm playing Mega Man Powered Up, a Capcom game. I haven't had the time to test with other games, though.
More on this issue: in the first few seconds of playing (Mega Man Powered Up in my case), the sound is great. A few seconds later, though, the sound quality and sound speed drop gradually to a certain low. Then the sound is slow, jittery/stuttering. The quality just flat-out deteriorates down to a low level.
Even more info: the sound especially stutters when there's a lot going on, on the screen. For example, if I'm on a menu with lots of animation, the sound quality drops. When I switch to another menu that's just a still image, the sound goes back to playing very nicely.
So it seems like the primary sound is taking a hit when the game is more busy. Any way to optimize the performance so this doesn't happen?