Glitches driving me Nuts!

OK I have a fairly old PC with XP and a Juli@ soundcard and RMAA audio analyser. This is used with the soundcard to do audio testing of external amplifiers etc.. through loopback on the soundcard.

It works great superficially. It gives a beautiful live spectrum graph with a nice low noise floor. However, every few seconds there is a 'glitch' and it's irregular the graph goes crazy before settling down again to a great display. I can just use this by working around the glitches. But all the main tests the system runs at the next level are swept over ~ 30seconds and the presence of the glitches makes the results worthless.

I can fiddle with sample rates /latency but with little improvement. I am thinking maybe something is going on in the background that might be interfering - what to switch off (and how) apart from the obvious LEXPPS..

anyone...