Now I believe the roaring sound has gone. After I pump my tires to 35 psi, the roaring sound disappered. Now the engine sound backs to normal and feel very good. I cannot think out any linkage between roaring engine sound and tire presure, but it really works on my X. Anyone of you who encounters this problem may have a try.

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--2004 E53 X5 4.8is - ECE version; right hand drive; Located in Hong Kong; ext. black sapphire metallic; int. leather black; adaptive dynamic bi-xenon headlights; 16:9 onboard monitor w/o navigation; 20" genuine BMW Y-spoke 214 wheels with Bridgestone Dueler H/P Sport tires; Int. rear view mirror w/ compass.