What causes the ping noise metal makes when its hot?

It is the sound metal can make as it expands. Makes the noise as areas can expand and contract at different rates. I.E. The chromium plating will expand and contract at a different rate than the steel it covers.

Spark knock or pinging is brought about even as 2 flame fronts interior the combustion chambers collide. The spark plug can commence one flame the front and the different is brought about by utilising a pointy nook interior the combustion chamber or a sparkling piece of carbon which ignites the gasoline air blend which crashes into the ignition of gasoline and air from the spark plug. in case you do not change the anti-knock sensor the valves, tops of pistons, piston earrings and piston ring lands overheat and capture holy hell. even as operating suited the anti-knock sensor reduces ignition timing hopefully preventing spark knock.

All sheet metal will ping as it changes temperature, because it is changing size. As it gets longer or shorter with change in temperature, it will have to change its bend between fixed attachment points. So then it is like one of those spring clickers they use to train dogs. Chrome may make more noise because the layers may have dissimilar expansion rates with temperature.

Its the confrontation of freqencies varring the molecular vibration of energy from heat to your ear!