SOLUTION (at least for me):
Not sure if this will help anyone else, but I have the same clicking and popping issue with my E17 when I use it with my notebook running Windows 7. It would start popping and clicking after a few minutes, the screen would flip between "USB" and the "lock" message and eventually the E17 would stop outputting music all together. Unplugging and plugging the E17 back in seems to reset the issue, but the popping would eventually come back. Changing USB ports made no difference (all the USB ports on my laptop connect to the same hub internally, that is shared with my mouse and built-in bluetooth adapter).
Curiously it only occurred if I am driving my Q701's and not my Reference X10's.
So, I thought it might be power related. I tried disabling the power management of the USB per other posts but that did nothing to resolve the issue. What I finally did was disable USB charging on the E17, and I have been running for the last hour pop-free! My guess is that my crappy work laptop is not providing enough power to charge and drive my "bigger" headphones at the same time. YAY!!!