my car has a knocking noise under the car ive had my tierods,ball joints upper and lower,link pins,stabiliezer bar bushings all replaced.when im driving and on freeway I can hear the knocking noise its not coming from engine but from undercar ive had 2 mecanics look the car over and neither can find the problem. can anyone help me out or point me in the right direction to find the problem.

 

There's no way other than getting under there to pinpoint where the noise is coming from. Something is loose and hitting something else. It could be just about anything: exhaust system, steering gear, engine mount, subframe mount, radiator, battery, who knows? Find a tall curb somewhere, drive one side of the car up on it and get under there with a good light and shake, pound wiggle and thump everything you can find, see or get to. You might see some shiny metal where parts are rubbing together. The heaviness of the "knocking noise" may give you a clue as to what to look for. Bigger parts make a different noise that lighter ones.
Shocks and struts can get noisy when they wear out. They might not show anything visible but if they have oil on the outside of them, they are probably bad.