2004 Chevy Colorado Weird occurances with truck.

I had trouble with the AC about a month ago and took it to a family member who works on vehicles and he looked at fuse box and said the fan fuse was not pushed in all the way and he pushed it back in and it works fine to this day. I started noticing that I would leave my keys on my counter at home and go outside and the truck alarm would be blaring and the radio would be playing at the same time. I would open the door and everything would silence. Tonight I walked outside on two occassions and the radio was blasting with no keys in the ignition. I opened the door and it silenced it again. What does the problem sound like and about how much would I be forking out to get it resolved? Thanks guys!