Ipod classic sudden sound distortion from dock connector only

I have an ipod classic 160gb 7th generation. When I docked it one day the sound was very distorted and unplayable. This happens in different docking stations yet they play with other ipods. I can still sync and charge (through some but not all chargers) and can play through headphones.

I have reset, restored, turned the EQ off and still no change. Any help /advice? not under warranty

thx