My harman/kardon sound sticks make crackling/cracking sound in the hi's when volume is up all the way, why?

When plugged into any of my computers, laptop or desk top, the 1" horns or high's tend to make a bad crackling sound when volume is turned up all the way. It has got to be the high's or the tweeters, and they are about 1 year old, purchased brand new.