Knocking noise, From the rear suspension. Options

[skogs]

Hi. I recently had some work done on my celica's rear suspension, the workshop replaced two rods, don't know what they are called in english, stabilisator rods or something? A rod with a ball on each end.
Anyway, a few km's after i got the car back, it started to make some really loud knocking noise when hitting even the smallest bumps in the road. I can really feel the knocking too. It seems that the knocking comes individually from both rear wheels\shocks.

I had the car back on the workshop and asked them what was wrong, and they blamed the exhaust-silencer's heat-shield, which is a little loose. Fastening that didn't help of course.

Does anyone have any ideas what could be causing these noises? I love my celica, and feel really bad everytime it knocks

would greatly appreciate some help!