That's good thinking, to test by turning off your anti-virus and internet connection. On one computer, I had to switch network interface cards to fix a problem.

If that doesn't stop the 'artifacts' you are hearing in your recordings, you could try running the DPC Latency Checker at http://www.thesycon.de/deu/latency_check.shtml It will show if there are any offending programs or drivers that affect your ability to work with digital audio. The site has good instructions.