One suggestion I read about getting rid of clicks and pops (bit errors in the digital stream) is to tweak/disable unnecessary XP services.

Here's a good site that outlines what services are running by default, what may be safe to disable or put in "manual" vs. "automatic", etc. As always, do the proper thing and set a restore point and/or export the services list.

Website for info: http://www.blackviper.com/WinXP/servicecfg.htm