Ipod model MCO34LL no sound in car USB

Hello,
Independently or with a head set I am able to hear the music from my ipod, but once it is hooked into an USB port i.e.my car, there is no sound. Everything else registers, songs etc. I tried a brand new cable, still no sound. This occurs in different USB ports so I know its not my vehicle's port. This happened all of sudden as it worked fine for years!