Playback is glitching out, how to fix?

I have a full drum and bugle corps score (brass, batterie, and front ensemble), and whenever I try to play the score with every instrument in, the audio starts glitching out and breaking down. I don't know how else to describe this, other than saying that it's a very harsh sound that messes with the playback. When I have just batterie and brass playing, it doesn't happen. It starts happening when I have all the percussion playing. I have bigger scores that don't have this issue, so I'm lost as to what is happening. Any help?