1994 Pontiac Firebird radio and sound system

This car is well taken care of, but the radio seems to want to function on its own. Some times the select wont work, same with the volum. Some of the speakers dont work all the time, and at times the only thing I here is crackling, very loud do to no volum control. This problem started a year ago, this car is kepted in side for the winter and is never driven in the winter.I havent tried to fix it yet, can you help give some ideas.