My sister has an 01 JGC with about 104,000 miles on it. Shortly after she bought it she had the front rotors replaced due to severe warping. Just a couple of weeks ago, she had the front tires replaced and the rear rotors replaced too, at the same time. Since then, she has reported (and I have experienced) a strange thumping noise under moderate to heavy braking. You can hear and feel thumps originating from the front of the vehicle, similar to running over a small stick (dia<0.5"). The thumps occur at irregular intervals, i.e. 3 thumps evenly, a couple of seconds of quiet, then one thump, quiet, two thumps, etc, all of which occur over multiple rotations of the tire. She brought the vehicle back to the shop that replaced the tires and rotors, they said it was a lump in the new tires that they couldn't correct. If so, it's not like any lump I've ever experienced, especially considering the irregularity and time-spacings of it. It can also be described as a "sharper" thump/sound than would occur with a tire lump, more along the lines of metal against something relatively hard.

I know the description is quite vague, but was all I could ascertain from the 15 minutes I had with the vehicle... so if anyone can think of anything that may cause this, please let me know. Thanks!