Whipple/Kenne Bell are both the same internals, ie Lysholm screw blowers.

I'd say a lot of the aftermarket stuff is made with making noise in mind too. The OEM would make them as silent as possible, whereas people retrofitting kits to their cars obviously want them to make noise.

Hell, Ive even seen people convert their accessory drive setups to a toothed belt to try and make a whine ! ( some with limited success lol )