A few personal experiences
Personal experiences:
(1) A PTT which deflected the engine RPM gauge by 1500 whenever I pressed it.
(2) A set of strobes which I discovered was transmitting on Middle Wallop's tower frequency when I called them up. Turned the strobes off, no problem. Any other frequency, no problem.
(3) A pax who'd left his mobile on, it was contentedly interfering with my intercom making it almost unuseable.
(4) I ran a "building" on a certain Secret-Squirrel airfield which was wired throughout with an aircraft technology (headets) intercom. Resonated frequently with the primary radar ¼ mile away. (Same site had signs at certain spots "no electrically operated explosives past this point", they weren't daft!).
(5) My own mobile routinely interferes with my car cassette player, but never with the radio. It also interferes with the phone on my desk at work if I put it down on that side.
(6) I have two phone (land) lines, recently put in at home. A call on one, can disrupt an internet connection on the other.
(7) A steel control column in a homebuilt which could deflect the compass by 45° with forward stick.
My conclusion - pretty much anything metallic, electrical or electronic can interfere with pretty much anything else. I'm not personally inclined to take chances and would prefer to leave unnecessary kit on the ground or off.
In the day-job I have routinely made myself unpopular by insisting on RF checks on strobes, shielding on pax entertainment systems, etc. So sue me!
G