Music Player in the car

I like to use my phone as my mp3 player since I always have it on me.  I just hooked up my car charger and 3.5mm audio input to the dongle today (I've heard complaints about the dongle, though I prefer 1 plug versus 2 for input + power.  anyway...) and noticed a weird variable tone warble behind the music.  I've experienced something similar to this before with the audio input which was fixed with a feedback loop isolator, so it shouldn't be that.  The tone isn't the same either.  After toying with it the warble went away when I unplugged the car charger.

Has anyone had any experience with this?  Would this be another feedback loop type problem?  My car charger is a generic one ordered off the internet.  Would a cheapo charger cause this?

Anyone have suggestions for a 3rd party mp3 player app?  The phones's mp3 player is ok, but I like to try a variety if they are available.

Thanks!