How do you connec the XP30 to your sound card - through line, mic or aux? From the way you describe it, your output volume of XP30 is too high and caused sever distortion on the sound card end. You may want to check your sound card input level is not set to be too sensitive (too high), make sure that you connect at line input, not mic input, lower the master volume slider on XP30. I usually use a good mixer between the sound card of the computer and the synth to ensure proper loudness.

Paul Ip
from Texas