Buzz when Side/Tail lights on ?!

I installed a new 29LTD radio with an external speaker.
Now, when my tail/side lights are on, there is a noticeable buzz coming from the external speaker. It does not change with the volume on the CB itself. Nothing else electrical/lighting causes a buzz or noise, just the tail lights....

This is all with the engine OFF, so it's not alternator whine or something.
I have no idea what could be causing this since the bulbs are all DC...

Anyone?!

 

Well, I did not nail this down. Removing the external speaker helps a ton.
It actually isnt hard to hear the CB while up inside the roof/visor area at all.

So while I didnt track this down, at least there is a work-around.

 

Yea..I did redo all of the tail lights..wiring and all. I had no tail lights a few days ago. 3 splices in these and all corroded.
Removed all splices and soldered all connections once and for all. I hate splices. They always fail at some point.
So the only left over lights to check are the 2 yellows on the front fenders, since I know the wiring is A1 perfect on the tail. I even bought all new tail light modules. There is no sound with the headlights or clearance lights. Only the side/tail/dash.

Since it doesnt bother me "NOW" - not sure if I will still pursue it