I had this once on a chevy. Out of round rotors and loose callipers. Every half turn the pads touched, the callipers moved (whump) but........
Could pad movement do this in case the calipers are good? Ie: touch, move, let go, touch, move, let go. If your pads are shimmying around perhaps? Seems far fetched, though.
But DO conduct the test outlined by Tim.
I had a dragging brake on the Van a few months ago and it was just hot and killed mileage. No 'whumping'.