probably dust and grime inside the control; With the ignition switch OFF,can you start the radio with the Volume Control? if yes, then disconnect the battery Ground, then turn the radioVolume/ON/OFF controlon-and-offabout 20 times, going through the complete rotation (to full volume) everytime and see if that helps clean it. (you don't want power to the radio while doing the above, since usually, the Volume control is also the On-Off switch).

If not,pulling the plastic knobs on the control and squirting a little WD-40 at the control shaft may also help clean it. No need to remove the radio for this.

 

Try getting one of those blower can things and blow some air in their as well.

 

you need to get tv tuner cleaner from radio shack, pull the knob off, it just slips right off. spray liberally with cleaner,this is probably a potentiometer, they require a little cleaning once in awhile. good motoring. Bill

 

Bill, I have used this TV Tuner Cleaner from Radio shack and I did not like it because it is too agressive, removing not just the dirt but the lubricant from the volume or tone control. Perhaps a TV Tuner control needs to be dry, but a Volume and Tone control in a radio need some type of "lube" in the resistance.
that's why I prefer WD-40.

Now, I am not a TV repair-person,but I swore I would never use that Radio Shack cleaner again, it actually ruined my equipment the time I used it. The control was never the same after spraying the TV Cleaner into it.

Jose