KB45 motor isn't notchy. Xerun 4274SL is. Why?

[Nixpus]

Hola amigos!

I had read before that quality brushless motors have a notchy feeling when the shaft is turned. So far I have only had my hand on the 1st gen Ezrun motors (4465SL) and KB45's... neither are notchy.

Yesterday I had a Xerun 4274SL in my hand and it was surely notchy... but why? The case is aluminium, the windings are copper. So whats the story... why is it notchy?