OK - here's the deal. I've got a 2008 F150 that I bought with ~40k miles on it. It's now at 150+k and have had very few problems with it. I'm on the positive end of mechanically inclined. In the snowpocapylse, had a weird thing happen - thumping when I came to a stop. Very definitely tied to wheel rotation speed. I thought it was ice, etc. and blew it off. So today, coming home from church, the truck started thumping when I put on the brakes at slow speeds. I thought, loose lug nuts, cracked rotors.... I jacked up all four corners and saw and heard nothing when I spun the wheels. Lug nuts tight, no obvious issues with the rotors, brake pads have plenty of meat, and the "problem" disappeared. Ideas?