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.