Exporting 5 min video consisting of 4 tracks, 2 video and 2 audio the resultant quality of audio is significantly worse than previewed original . Tried exporting to MP4 and Windows wmv format. Same results.

I kept the format in export setting same as movie setting.

System: Compaq P4, 3GIG MEM, ATA HDrive, Integrated Intel Graphics

Any clues? 

I did apply effects but returned the audio track back to default before exporting. I'm wondering whether the export engine is trying to export failed effects?