2001 Volkswagen Golf knocking rear end

See if you can get the shocks to bounce, just put some weight on the bumpers; the shocks should go down and come up once. If the car bounces more than once you probably have one or more bad shocks and should replace them, what I see happening is every time you hit a bump one of your shocks is compressing completely and slamming itself against your frame causing a loud thump.

If the shocks are all good, check to see if you have a loose brake pad.