96 Jimmy radio, erratic volume issues

[blackknife]

recently I noticed that when I turn on my stock equipment Delco radio/CD player, the volume didn't work, then suddenly it went up very loud. So I turned it off, tried again, but it did the same thing, and I have no control over it at all.

I also had some issues where if I didn't run the truck for a few weeks, the battery would be almost dead, so I replaced the battery. I got 14V with a multi-meter at the battery posts with it running, so I assume my alternator is ok, although it's been taking longer than normal to start when cranking, when it used to start right up. Not sure if anything is related.