What causes my car's charging system indicator lights on and chimes once in a while?

My car chevy malibu model 2002 charging system indicator light goes on and can hear a chime once in a while these few days. Alternator working nicely even when air con, radio and lights are on. the only electrical problem i know is that the air con switch is loose and goes off now and then. Need help. Do i have to change the alternator or what. Thanks a lot