The thumping was the tires trying to slide but grabbing like wheel hop on acceleration. I have abs in my 96 GMC pickup and it acts totally different when you slam the brakes before the skid the brakes pulse and then let up so you dont skid and there is always that weird zuuuhhh sound when that happens. The Crossfire just stops no pulse or let up but these tires wont skid smooth on the rough asphalt in my neighborhood they grab well. I am sure the ABS is not working. It would be real easy to tell on water huh?