[bepperb]

Warped Rotors
Tires out of balance
Tire belt problem
Strut issue

So the of the potential solutions, the free one is rotating the tires and checking if there is a difference in performance. While you're in there, check for a pattern of deposits on the rotors. As stated, you can't see warping but I've seen some rotors that were obviously the problem. Also, check that pad wear is even on the inside and outside pads.

All that is free. Based on what you see will determine what I would do next. If the tire rotation fixes the problem, you're set. If not, the condition of the tires and brakes would determine if I would get the rotors turned, get new rotors, or an alignment (or all of the above) and perhaps even new tires.