New Windows XP CD/DVD drive slows down...

I recently purchased a Dell Inspiron 530 Desktop PC with Windows XP. Without any obvious cause the CD drive started playing up and intermittantly slows down for a fraction of time while playing and ripping CDs. Even DVDs slow down.

Dell ran full diagnostics and no malfunctions wre detected. A Dell technician replace teh CD hardware with a new CD drive and the problem persisted. Eventually the Dell technician re-installed Windows XP and when we tested the CD /DVD it worked OK. However, as I reinstalled the applications' software and back up data the problem reappeared.

The PC system has a Realteck Sound Manager and a Nvidia Sound Card.

Any ideas of how I can overcome this problem?

Thanks