My car has recently started making some bad sounding noises upon startup from cold. When you start it up, you get a banging/knocking noise for the first 30-60 seconds, then it quietens down and seems fine. During this period it seems less willing to rev.
It only does it when its been left for 8-12 hours, if you start it up after say 3-4 hours of being sat it starts fine with no noises.
There are no warning/lights on the dashboard, and it seems to drive ok once you get past this stage.
See end of post for a you tube video, you'll have to turn the volume up because my phone didnt capture the sound very well.
I've got a few ideas of what it could be , but would appreciate any ideas you may have.
Car is a 2008 m3 with 37000miles, and is totally stock, no modifications at all.