Mess with the sound buffer
Set it at the highest (7) and reduce it until the sound is fine
The sound code is different from previous version's and the buffer actually does something
I set mine at 2, with your system try it a little higher and see if it does the job.
I remember with my other system (366 celeron, 64mb) I had
to run it at 640x480 with scanlines to get resonable sound. Using double line mode is far more processor hungry than using scanlines AFAIK.
Edit: Damn spelling's