I have a thin tinny sort of rattle from under the hood. The cat heat shield long since fell off, so not that. Had daughter listen while I raced the engine a few times, but it doesn't seem to make the noise under no load conditions. I seem to get the noise most obviously when I downshift to 2nd and apply some throttle, when the engine is at fairly low RPM and under some load. I looked at the famous firewall bracket, but it isn't broken and doesn't make noise at no load. Any guesses??