For what it is worth, my Toyota had a start up pinging noise, only first thing in the morning, and that went away when the engine was warm. It was a pin hole leak in the exhaust manifold gasket.
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E