E90/E91/E92/E93 (2006 - 2013)
Every morning at start up, the engine pings/knocks as the RPM's are slowing from a rev up. It only happens for the first 2 or 3 minutes, whether its cold or hot outside. It goes away very quickly. It has happened after sitting for an hour or so, but goes away quickly.
I made a little video...