I am as well with my 24 inch iMac (white, c2d) and external unshielded speakers. It was happening with my iphone in close proximity, but the popping wasn't the normal gsm noise.
Coincidentally, the popping fit perfectly to the beat of "Blackbird".
yes i have it, it happens right before a sound happens, only if its silent for above a minute or 2, it really doesn't bother me, i normally have music playing so the speakers are always running.