My cooper S 2008 has devoped a rattle from the engine this week. It happens after around 5 minutes once the engine has warmed up. Once over 2000rpm it rattles like hell. Oil level has been checked and is at full. Its off to the dealer on Tuesday.
It might be a tensioner issue at that kind of revs, quite a common issue on this engine. I had mine changed earlier this year (2008 MCS on 35k miles), they changed the chain, tensionners, sprocket, etc etc Good job I had the extended warranty.