Lights Dim out once in awhile

[SaberZ]

on my impala if im driving at night the headlights dim out for less than a second(like high output an it goes low for sec an goes back up) once in awhile. Some people said that I need to tighten some screw or bolt on the altinator or something? Anyone know what it might be on a 3800 Series II. Rather do it myself instead of going to the dealer and waiting for my car to come back out. Or at least try to do it, then send it to them.