Hi everyone, it's been a long time since I've posted here because most problems I can now diagnose and fix myself. But this one has me stumped. I just replaced a leaking water pump and radiator, and drove the car 100 miles roundtrip: it performed flawlessly. About 2 minutes from home, at highway speeds, I heard a metallic 'chipping' sound coming from the engine. No idiot lights, overheating, or otherwise abnormal signals from the gauges. No loss of engine performance. I pulled off the highway, up a hill towards my house, the car pulled just fine, just this annoying metallic sound. But then, at the top of the hill, the car died and fortunately there was a parking spot right there that I coasted into. I popped the hood, and everything looked fine. It started right up again, with the annoying metallic sound still present. It's not constant, it sounds like something is flying around either in the engine or the cooling system. Or possibly a very bad ping?

Anyway, I'm wondering if anyone has experienced anything like this. The new pump was a bit noisy when I first installed it, but has since quieted right down. Is it possible that something broke off from the impeller and is being kicked around in there, causing the knock sensor to overreact? It's a turbo car - possible a similar thing could happen there? Valvetrain? big end? It's difficult to tell where this sound is actually coming from...

Any suggestions most appreciated! If I can't fix it soon, this car's going out to pasture, I'm afraid.... Thanks!