BMW have a bulletin out about the hydraulic valve lifters making noise on first start up from cold. They blame lifter failure on infrequent oil changes or too high a viscosity of oil being used. Noises are difficult to guess at without being able to hear them first hand. Any time you hear an abnormal engine noise check the engine oil level.
After that your engine has hydraulic lifters that automatically adjust the intake and exhaust valve clearance using engine oil pressure when the engine is running. Engines with hydraulic lifters need to have oil changes at the recommended intervals to keep the oil clean and fresh and the correct weight or viscosity of engine oil . A small bit of dirt or sludge can "gum" up the lifters and cause the oil not to properly adjust valve clearances. Sometimes this noise goes away after initial start up or after the engine warms up. If it is as simple as "lifter noise" try adding an oil additive called Risolene, it is a low viscosity high detergentcy oil additive that helps clean lifters. Of course an engine knocking sound may be a sign of more serious engine lubrication problems that could result in catastrophic engine failure so get this checked out .
Don't think it's the lifters sounds more like its coming from the cam. It's more like a clicking clacking noise that seems to have gotten a little louder in the last 3,000 miles. Thanks for your help.