You're wasting your time trying different oils, the rattle you're are hearing is called Vaonos rattle. Do a search hear or on Google and you'll find tons of info about this subject. The only way to permanently get rid of the noise is to rebuild the units and install the new improved seals or buy new aftermarket units with the improved seals already installed. The noise doesn't hurt anything and BMW was well aware of the problem in the late 90's, it affects mostly the V8 engines. If you replace VANOS units I would also replace the little oil anti-drainback valves, replacing them alone though will not fix the problem. By the way my X5 has that noise also, but it runs perfectly fine with over 200K on the odometer.

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2002 X5 4.6is
1999 C5 Corvette
1992 Mitsubishi 3000GT VR-4
1994 Kawasaki ZX-9R
2005 Mazda 6 Wagon (Wife's)
1991 Mitsubishi 3000GT VR-4