Not really an idea or solution, but more info is usually better.
I experience something similar, On both the LG quantum i had, and my Samsung Focus. When i plug into the USB in my car it goes through a continuous cycle.
Seems as if it's charging, then car radio auto changes to aux,then phone makes sound as if you just plugged in, radio goes back to previous setting.then radio changes to aux again over and over.
Suspect it has to do with radio looking for a mass storage device, but when it doesn't find one why does it retry.