There is a clatter sound coming from the engine of my 528i whenever it has been used for say, more than an hour and revs had gone up close to redline. Temp never goes up from midpoint, I get no warnings from the computer or whatsoever, and the engine idles and runs normally. The clatter sometimes becomes evident at startup for a few seconds but I've read here that this is normal, then it quiets and comes back stronger, it is so loud it sounds like a diesel. If I wait for the engine to cool down, for example overnight, and then start it again, the clatter is gone. What could this be? VANOS? :-S