Recently the engine mounts were replaced and idk what this idiot mechanic did but he screwed me over big time... Whenever i put the car in reverse when its idling over 1 RPM it will Knock very abruptly and loud, and then if im reversing fast or up a hill it knocks the whole time as if the car is going to fall apart. What is wrong, what can i do to fix it??? PLEASE HELP!