FM Interference

LED's themselves are "clean" electrically but the "driver" circuitry which controls them may not be. "Pulse-width modulation" is often used to regulate their brightness and much like switching power supplies the same thing occurs in PWM drivers.

From a manufacturer's point of view it's not hard or expensive to incorporate shielding into the outer cases of their products, but when you confine the EM radiation inside the device it can sometimes cause some very weird reactions with components and circuits inside the shielding. When I get around to doing the testing I mentioned earlier I will look into this as well, hopefully within a couple weeks.

Phil
 
I just thought I would come and update this thread now that I have finally (mostly) managed to fix the problem.

I have now gone with a new cigarette lighter wired in to the power to the interior light in the headlining, with a Wicked Chili USB converter along with a shielded 50cm USB cable. Because the cable is not running very far around the car the problems seems to be mostly gone. I can still hear a very faint crackle when I drive down the part of the motorway that I used to lose signal entirely, but only very faint so a definite improvement.
 
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