AV Cable with USB Charging?

[undrstm8ed]

That is because they do not share common ground creating what's called a ground loop. Typically a thin wire going from vehicle ground, shared with charger grounding could cure that. However, each scenario and vehicle with equipment will change that and each case would be not so fun factors to chase down...

 

[undrstm8ed]

I am currently working on flush mounting a Galaxy Tab3 in to the dash board of a Ford Ranger and having to overcome some small issues such as this.