Either front upper control arm bushings or the kingpin joint (bearings or a worn kingpin). Other place to look is to make sure that your new rotors are not hanging up on the center bore of the hub instead of mating flat on the hub face surface. Have a close look at your inner tie rod ends (and everything else) with the strut lower mount disconnected and the suspension held at ride height with the car body on jack stands and the front suspension supported by a jack or block under the lower control arm.
What suspension mods do you have on the front? What style of tension rods?