I have a 98 gmc truck that started having problems a few weeks ago. I took it to a mechanic just to get a better idea on what’s going on. The mechanic said it may be a flexplate/flywheel, or maybe valves. The problem is that there’s a knocking noise coming from the truck somewhere whenever I accelerate, but soon as I let go of the gas, it stops. The knocking increases with speed, but doesn’t knock when i coast. Any ideas on if it is the flexplate/flywheel it has to do with the engine itself? Need some help from those who had similar or the same type of problem. Whatever the problem is, is it better to save money to fix it myself or just take it to the shop? Was quoted $600+ for repairs on whatever the problem is.