2001 Mazda 626 Knocking noise from underneath car

I have a 2001 Mazda 626 with 100,200 miles I just purchased. The only issue with the car is when I go over bumps, I hear a loud knocking sound that sounds like ehaust is loose. Had it ckecked out and it seems fine. The shocks are slightly worn on the back passenger side but only slightly. The noise is barely noticeable when I have a passenger with me or someone heavier drives the car. It seems the more weight, the less bumping noise from underneath. I also notices vibration in the steering wheel.