hmm... All I can suggest is maybe looking at task manager before and after see if theres anything that changes in the stuff thats running, see what programs are in memory that may look suspect, You would think It have something to do with your sound, but you said you took out your sound card... Is the sound coming thru a speaker in the computer or speakers hook to your sound card? Thats some strange stuff I havent seen it do before. Id just keep looking and see if you can find a setting or something somewhere.. For fun disable windows sounds and see if it stops... It should...
Civic Addict is a Windows 2000 man, maybe he may have some suggestions..