With the help of a good avionics friend, we recently found that some of the little GPS pucker did interfere with my radio when powered (and connected to a Kobo), while other models (we switched to a dongle) didn’t.

It took a long systematic one by one elimination test, turning on and off one device at a time. One source of static can be your phone(s) obviously, so your testing must include those. Once you find the culprit the solution is probably simple or already explained by some of the pros above who know electronic better.

Good luck,
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