From what I read here on the site it's just the Vanos, there's a thread about this so do a search. It gets noisy on high mileage vehicles, rod knock would not go away after a few seconds.

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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