I've tried at least 5 chargers from generic $5 ones from Lowes (2amp), Droid X, wife's Razr Maxx, VZW sold Belkin 2.1 amp, Motorola usb generic for my droid x car dock, and all work fine. Perhaps a bad charger?
Make sure you get a high power one. 5" screen, 3100 battery, and using GPS, LTE, split the screen and do a movie and GPS at the same time as the kids in the back seat connect to you via wifi for tethering, you will need a decent charger.
My cheap $5 one worked fine, but was dirty. You could hear a hiss in the car speakers when using the headphone out jack to the car. Unplug the charger, hiss goes away. Replaced with the belkin 2.1 amp and no more hiss.