OKAY GUYS, here's what's going on.
Your car has a "ground" (in electrical terms), and when your phone is charging, the charger, or your phone's battery, or whatever, also has a "ground". Usually, ground is supposed to be the same, but in truth, it isn't always, and that causes a ground loop
Ground loop (electricity) - Wikipedia, the free encyclopedia
YOUR PHONE IS NOT DEFECTIVE, this buzz is totally normal with GSM/EDGE/LTE, but shouldn't happen with 3G/HSPA/CMDA because of the technology. The cell radio turns on and off at ~800Hz, which is audible. It is not because of the cell phone frequency (which is 700-1900 MHz, which is wayyyyy too high frequency to hear). A shielded cable won't fix the issue and there's nothing wrong with your car, or the phone, or anything else.
-Geobio