I have a 1992 Chevy K1500 with a TBI 350. A little while ago a developed this metallic/metal on metal scraping/knocking noise. At first I thought it was a U joint or spark knock so I replaced the rear u-joint, distributor, cap, rotor, plugs, wires, egr valve, ignition module, and knock sensor, and readjusted the valves. Yes it is set at the correct timing, no the timing does not jump. It will only make this noise while in drive or reverse. I can rev all the way up to the swirlports redline in park or neutral and it will not make this noise. And ideas will be greatly appreciated as I am stumped.