High Pitched Whine With Powered Audio Signal

I have an 05 LGT 5MT with a Jazzy Engineering mod to the stereo for an aux input.

 

Here's the problem I have. When playing music from my phone using the 3.5mm aux jack, everything sounds fine. However, when I charge the phone using the cigarette lighter/DC power port in the console and play audio from the phone through the aux jack at the same time, I get a high pitched whine in the background that increases with the speed of the engine.

 

Overall, this wouldn't be a big deal, as I very rarely need to charge my phone while playing audio from it. Problem is, a recently got a bluetooth audio receiver which I installed in the console and needs to be powered all of the time through the DC power port. I really like having bluetooth connectivity and it works great, but any type of audio signal coming from a device also powered through the DC port has the same whine.

 

I'm guessing this is some kind of electrical interference, probably related to grounding of the power port. Thoughts?

Little late but i'll add to this now, its a weak ground you have to the power port, you are on the right track. Try adding a 2nd ground wire to the power port.