USB Soundcards - faint popping/clicks

I am currently using a G4 iBook 933 MHz and have my new Waveterminal U24 connected to a DAC and Headphone Amplifier. The sound is really fantastic. I do notice every minute or so, I get a very faint pop or click sound. Sometimes I go longer without hearing it, but it occurs often enough that I notice it. I have tried to research this and there seems to be an opinion that this is just a USB audio problem and nothing can be done. I have experimented with settings. I have more than enough RAM than I know what to do with. I am using iTunes and so there really aren't any settings to adjust there except turning off all of the enhancements.

Anyway, anybody have any suggestions for USB audio pops?