Knocking

My car has had it's first MOT in October and had to have a rear shock replaced. But since then my car has had other issues.
I get a knocking sound from the offside rear. I've had it checked at several garages. but they can't find whats wrong. The shock is ok, no wear or tear anywhere and nothing loose.
When on an uneven road it will knock really bad and when I go right hand down and put forse onto the leftside of the car it knocks.
It sounds like someone is banging a big metal spanner on the metal frame if this helps with what it could be. I am confused but worried as well. :confused:
Any clues what this could be as I really do not want to take her to the main dealer. Just can't afford that.