My HID's are attached to a 4 pin relay connected to the parking lights for a +12 source, for the longest time it has resulted in a noise fed back through my tweeters (even though the amplifiers are not turned on)

If I sit in the car and press any button on my key fob, a high pitched noise will appear and go off at the same time as the light flash through my tweeters (car off, no key in ignition)

For the longest time I had stumbled upon "protection diodes" thought of it, but never actually tried.

Conclusion: simple fix, attach cathode = k = striped end of diode (pin 85), now wait for it, attach the other end of the diode to (pin 86)

I'm now reading that the voltage spike caused by de-energizing the coil in a relay results in "back EMF" which can be nearly 200V!!!

I'm guessing that was what I was hearing.

If you've got relays, couldn't hurt to spend a few dollars on a box full of diodes

 

I recommend when tapping on to anything from the factory bcm that you put in a protection diode for this exact reason.

I had a similar situation (not noise) where my headlight output (from my cluster, in this case) would turn on a relay that subsequently turned on my HIDs. Now, when I turned off the headlights, the HIDs would stay on until I disconnected the relay. Adding a protection diode to the relay fixed the problem tout-suite.

Transistorized circuits are finicky bastards :P