nifty fifty "clicks"

Okay, soooo my nifty fifty has become my hands down favorite lens (out of the two LOL) but all of a sudden it started "clicking" when it focused... what's the deal... it's not jittery or anything, the 'action' is smooth (at least through the viewfinder). What on earth is going on?! it didn't do that when I first got it

mine clicks, I think, when the focus motor changes direction

it's a continuous thing, it's not like it's slipping or anything.
It clicks from the very front focus to the very back....

i noticed the same thing with my 15mm fisheye. it clicks when i first attach it to my camera. not necessarily when I'm focusing but it just randomly clicks