Are you using Midi or RealDrums? If Midi, there may be some events in the drum track causing this.

The R Audio will create the file in the same directory as the song. After you Save it, the WAV will have the same file name as your song. If you leave the WAV there, it will play along with your song thus duplicating everything. Probably best to move the WAV if you like the result.

You may have to use your built-in sound card for the R Audio.

R