I'm using CS3, with a sequence with multiple audio tracks. After exporting to mpeg-dvd, the audio where the second track kicks in, it sounds distorted. It sounds fine when previewing, and also when I exported only the specific work area. But once I export the entire sequence, it sounds bad again (at the specific area). Does anyone have any ideas to resolve this?

What audio bitrate are you expoting to mpeg? The higher the better, up to a point. You should be exporting at LEAST 32 bit.
Also, how have you mixed the audio? You might that audio track at a higher level in your submix to your master....

Do you have a Matrox card with your PP? If so, then don't forget to have your Audio Hardware preferences set to Matrox . . . not Premiere Pro. This is often the reason for the problem you described.