1997 Chevrolet Camaro my alternator keeps going bad

1997 Chevrolet Camaro mileage: 154,000. What could be the reason (s) that my alternator keeps going bad? I have had three put on since I bought the car in 1995. And I don't know if this is related to the above problem, but I cannot leave my car sit for a couple of days without being started and driven, or the battery goes dead. I have bought three batteries in the past four years also. Sometimes when the stereo's off, I can hear static and engine through my speakers. In case it is of importance, my stereo was installed in 1995.