I recently purchased a 5.0L/302 GT-40 Aluminum head long block engine assembly (P/N M-6007-XB3M) from Ford Motorsports. The engine was installed by a reputable shop. Upon picking up the car (1994 Mustang GT), I had a very obvious valve train noise from the r/s of the engine. Ran the engine approx 100 miles and noise did not subside. Changed the oil (20W50) and there was no abnormal particles in the oil. Drove engine another 75 miles and noise continued to get louder. Had towed back to installer. Roller rocker and valve lash were checked 2 times and no problems were found with upper valve rocker train. We suspected valve guides are too tight but we are unable to pinpoint tapping noise. Changed oil again, cut oil filter open and no debris (silver or gold) detected. Has anyone else had a similar experience or could point me in the right direction.