REAR Brakes (no, not another lever travel thread)

I recently started to notice that, when coming to a stop from low speed and applying a little rear brake, the pedal seems to pulse. It's weird and I never noticed it before. It doesn't feel like warped rotor, and it's only noticeable at very low speed approaching a full stop. The brake never was much good at adding stopping power to the fronts but I never noticed this before. Anyone else ever notice something like this? Ideas?