Tuff Stuff 100 amp alt whistle

Huh. I've got a couple of tuffstuff 100 amp alternators, one on my Duster with a serpentine set up and one on my Challenger with a v-belt. They definitely aren't the quietest alternators I've ever had, there's a bit more whine/hum to them than a stocker. But no shrill noisies when revving the engine.