Metal Slug problem

I have a PAR+ and am having a problem with Metal Slug. While playing only the music at the beginning of a stage plays then keeps looping over and over. I've play the arcade version and it doesn't do this. The same think happens at bosses, it's like the first few bars just keep repeating. If I go to sound test they play properly though.

So, do you know if it would be a problem with my PAR+ or the game? (I don't have any other 1mb games to test it with, only 4m ones)

is it a burned copy? if it is, check the audio tracks on your pc first. other than that, it sounds like a scratched disk, or mayby a dirty laser
Is your game a burned copy?

I downloaded a rip of it myself and found that some idiot completely messed up the audio tracks. Most of them start and end in the middle, and the lengths aren't right at all. I've yet to sit down and fix them with Sound Forge before burning the game.
Yeah, it's a burn. But I don't have the files on my comp anymore to check. So I'm guessing it's te burn or the cd rather than my ram. Does anyone have a real copy to tell me if it sounds right?
I played it on my comp, and the tracks were screwed up just like in the game. So, it was the burn.

EDIT: I found another copy, burnt it and the sound is perfect. Thanks for the help everyone.
Same here I have a PAR+ and a copy of metal slug that was d/led from elportal. It happens the same thing the sound just loops in some stages bosses.