Some suggestions:
- reset to factory as has been suggested
- change tempo to 140 or higher. You are stretching the tempo lower (140-130), which can introduce artifacts (Elastique stretching engine)
- try enabling Prefs-RealTracks-High Quality Pitch Shift
- (since you report that the rendered files sound fine) right click on combo, and choose "Render Song to Audio Track" - then you will hear a rendered version, which may have less artifacts.
- (since you report that the rendered files sound fine) Use RealBand, which renders the tracks first. RealBand will open your BB songs, you just run RealBand, choose File-Open and then press the BB button to generate the song.

Have Fun!
Peter Gannon
PG Music Inc.