Truck: 1993 Chevy C-1500 Half Ton, 4.3 V6, Automatic transmission
Problem: When accelerating there is a loud tapping sound from the engine area. It sounds like a metal part. I can drive about 1/4 of a mile before it starts. I recently replaced both motor mounts and, later, the transmission mount. I thought the oil pan may have been bent inwards when doing that job, but the noise did not start until a week or two later. The transmission mount was replaced after the noise started. The noise sounds like something hitting the bottom of one of the pans and does seem to come from the lower part of the engine. I cannot get the sound by revving up the engine while in Park. It only does it when it is actually moving. Because of that I ruled out, possibly incorrectly, an exhaust leak. I have also ruled out the fan hitting the shroud, because I removed the entire shroud, drove it a short distance, and heard the noise. The noise seems to follow the movement of the truck (e.g. when I'm accelerating there are dips in the road, the up-and-down movement causes the sound to get louder and quieter in line with the truck itself). I have not noticed any problems with oil pressure or temperature.
I know this is a long winded explanation, but I really hate taking my vehicles to a shop. Any ideas would be appreciated.
ATL