1991 Z28, it's a 5-speed, around 96k on it. New inectors, full tune up and fresh fluilds, all filters, oil pan seal, differential flush and new seal. Car is running rich, and misses occasionally at highway speeds due to an EGR valve being clogged. Car was extremely well mantained and is in really nice condition, but since I've owned it, it's used oil. Not consistantly, but sometimes as much as a quart or more in 150 miles! It runs pretty good, its really quick. But, I have noticed that when the hood is propped, and you rev it with the throttle on the intake, you can hear a notice scrap/knocking sound. It's silent at idle. The car does need new clamps for the manifold to midpipe, and has an exhaust leak, but I am skeptical that it is an exhaust leak that is causing that. The noise isn't really noticeable when driving the car, it sounds pretty good. The knock sounds like it is coming from the engine. Any ideas? Similar issues? It's been used as a daily driver for a month now, and I haven't had any issues with it and that sound doesn't seem to be any worse after 1,000 miles.