I have an Apogee Duet 2 and I always get this popping/clicking sound. I don't think it's ever happened when recording or playback, but it happens in iTunes ALL the time. Sometimes I'll unplug everything and plug it back in and it goes away. The other day I had to restart my computer. I'm not sure if this is an issue with my macbook , iTunes, or my Apogee... but it happens VERY often and it's really annoying. Has anyone else experienced this? Any recommendations? Thanks in advance!