I have an '01 X5 4.4i with 107k and it makes the hard knocking sound as well, it also did it when I first bought it with 97k.
I've read that it has something to do with Vanos (automobile variable valve timing technology developed by BMW).
Changing the oil and adding a bottle of Lucas helped it. Didn't take the knock away fully, but definitely helped.
Hope this helps!
Brodie Morris | Morris Racing
2001 BMW X5 4.4i - Jet Black - Beige Leather - Sports Pkg, Cold Weather Pkg, 20" Aftermarket Wheels
2002 BMW 745i - Sterling Grey Metallic - Black Leather - Convenience Pkg - Sold
1999 Chevrolet Corvette - Arctic White - Tan Leather - Convertible - Sold
2006 Chrysler 300 SRT8 - Silver Steel Metallic - Black Leather - 425HP, Navigation - Sold
Last edited by BM0rri5; 05-24-2012 at 01:56 PM.