Alot of this is due to grounding methods. Interestingly, a test recently conducted showed that having a ground (one that literally went into the ground) horrendously increased rf interference. They began to look at why, and saw that most of the pro audio devices had a grounding method that was inadequate - mics being grounded to the shielding as they should, but also jumped across the circuit boards - this being the main source of issue. I forget who did the study, but there is a whitepaper out there. I don't have it at home, but I do have it at work - I will be back there tomorrow (home sick) and will post up a link to it then. Lots of info is packed in there. As a note, the one interesting thing that came from this was a line of mics that were "blackberry-proof". I'll have to remember who made those, it may be of interest as well. -Joseph M. Gaffney
