I have a question. 1999 chevy Silverado, 1500 extended cab ls model. 2 days ago r & r the valve cover gaskets. ever since then I notice a pinging sound when driving down the road. back in the day when you had a metal shroud and metal fan fins. the shroud or fins wound become loose, so you would tighten down the shroud or fins. this is the same sound I'm hearing, ( pinging ). I had a friend put the truck up on the lift and check everywhere, nothing. no sound while in neutral, I press on the pedal nothing. I can put the truck and put foot on the brake and give it a little gas and the pinging starts. It sounds as it were coming from the bell housing, check that, nothing. I thought maybe a screw maybe had fallen in between the exhaust guard and the engine, nothing. now it's not a constant ping I can be cruising and give it some gas and then you hear it for that split second or two, then nothing? ) only when the engine is engage, not neutral or park. ) Thanks... The Engine is nice and strong, no lose of compression, no missing. so nothing was dropped on the top side of the block while uncovered.