Several years ago, we had a Citation 550 in our fleet that experienced a complete loss of COM radio functionality whenever flying in visible moisture. (Especially snow). A loud hissing noise was heard in the radios that would drown out all incoming transmissions.
We replaced all static wicks, reworked the mounting plates etc, all to no effect. We finally took the aircraft to the Citation service center at KSWF, who had a machine to emulate the static charge conditions found in flight. It was a high-voltage generator, that connected to an insulated wand that was passed over the skin of the aircraft from nose to tail, while a tech inside of the aircraft monitored the COM radios.
The test quickly pinpointed the radome as being the source of the problem. The aircraft's original radome had been damaged in a towing accident, and a rebuilt radome fitted, shortly before we took delivery. It turned out that when the radome was rebuilt, the overhaul facility missed a critical step, and as a result, the 6 static diverter strips embedded in the fiberglass had no physical electrical connection to their airframe bonding pads. Once that was corrected, never had a problem with p-static again.
The skin mapping machine at the service center required a great deal of care and training in operation, as it apparently generated lethal amounts of high voltage.
At my current employer (Part 91 corporate) our aircraft have a 12-month inspection requirement for static wick bonding and resistance checks. It's not unusual to find one or two (out of 16) that fail the resistance checks during the inspections.