On my 94 I have a noise. I thought it was pinging. Switched to hi-test fuel. No difference. Could be a rattle. Thought maybe a heat shield. Can't find a loose one. Makes the noise under load. Not evident with slow acceleration on the flat. Omnipresent under heavy acceleration or uphill. Any good ideas on how to chase it down? My check engine light comes on frequently but everytime I've checked it, it's the EGR code.