I agree with fleecerdog and the senator. I believe this car was a Jeep with the 3 second delay clunk and felt like he was bumped from behind.
If the drive shaft yoke splines are dry and rusty this could stick in place w holding the suspension slightly loaded after coming to a stop. When the weight of the vehicle finally overcoms the stuck splined it shifts (telescopes) and goes clunk.
I am not sure if this vehicle has a telescopic splined drive shaft or a splined yoke on the trans output shaft.
I would pull the drive shaft and, clean and grease the splines and recheck for clunk/bump.