first of all, what engine do you have? 3.0 or 4.4? second, the sound of stock exhaust is just fine, you dont need more rumble to it. well, it depends on your taste. i dont want any more noise than it is already is, so i installed the 4.6/4.8is tips on my 3.0 last year. i just want the look. it doesnt matter what kind of exhaust system you use, it is not gonna give you a lot of power on an 3.0. so why bother spending thousand on the whole new system.

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2002 X5 3.0 Siena Red
Premium, Cold Weather, Rear Climate Packages, 19" Wheels
Aluminum Running Boards, Clear Tail Lights, Clear Side Markers
Titanium Kidney Grills, Titanium Trunk Lid, Xenon Headlights
4.6is X5 exhausts, 35% Tint, Aluminum Pedals
2005 530I Mystic Blue
Premium Package, Sport Package, Xenon Headlights
18" Sport Wheels, 35% Tint all around
Mods to come: M-Tech Front Bumper, M5 Side Skirts, M5 Rear Bumper
Quad Exhausts, Style 172 19" Wheels