Hello to all,i have a 3dr sierra cosworth,and i have a noise for example with 4th gear from 3000rpms - 2600rpms when i leave the throttle ,from under the car about in the end of gearbox and in the rear place like grrrrrrr like something metalic part have vibration or something knocking and comes noise, all the parts are new, drive joints,rebuild prop-shaft with all new,rebuild gearbox,rear diff with 65000km,wheels bearings new,also i tested the car with SAE140 gear oil and the noise still there,so does anyone had the same issue?any idea? thanks in advance

Thanasis