Car Suspension Noises on Bumps

Hi,
'On my 1995 Golf 3 (1Z), I'm experiencing really harsh jolts at the rear axle. For example, when I drive over a ramp with about a 3cm lip, or when I hit a slightly raised manhole cover, I feel a hard impact throughout the body of the car. The shock absorber test at ATU was successful, but they didn't have time for a test drive.'
Does anyone have any idea what this could be?

It's not *that* important, since a different suspension will be installed in the near future, but it's still a bit annoying.