It's a common problem with new ate shock they knock all the time as the grease goes hard and the inside of the shock binds and makes it sounds like there gone . Look up Asd on here in the market place section he does a regreese and fits a grease nipple better that buying new shocks if there not gone
Jack up the back of the car and the the wheels hang down And the shocks will be fully extended then lift the black plastic sleve and spray in some white lithium grease it should stop the knocking short term