Originally Posted by FifthStreetz
what do you guys think is the cause of the noise?
I personally believe that it sounds like timing chain slap. There are valves on the hydraulic timing chain tensioners that hold in oil pressure to keep the chain tight while the engine is off. If the valves on the tensioners go bad, the oil pressure will bleed off allowing the chain to become a little loose. When the engine first starts and oil pressure is low, the chain will rattle until oil pressure builds up and reapplies pressure to the tensioners and chain.
BMW seems to agree. They are changing my timing chain tensioners as we speak. However, another member posted that this didn't solve his problem. In one case, replacing the VANOS check valves seemed to do the trick but that didn't work in another. From what I understand, there are pins on the VANOS that lock the system in place when the engine is off in which case the check valves don't come into play at start up. Again, my dealer/BMW seems to agree with this. They disabled the VANOS system (disconnected the VANOS solenoid IIRC?) and the problem was still present.
edit: I should also mention that nothing suggests that this is a bearing issue.