Originally Posted by xrwrx (Post 687052)

....
i am having this problem for a while. when i backout of my garage, while turning my can towards left. i can hear some 'knocking sound" coming out of the front undercarriage, sound like from the front wheels area or suspension.....
anyone has similar problem ??

Originally Posted by FunfDreisig (Post 687388)

Does this only happen at low speed on uneven terrain? Is the knocking sound only a few 'irregular knocks' or is it several more 'rhythmic knocks'?

FWIW BMW techs are paid to replace obviously broken stuff quickly, not diagnose intermittent problems.

Funf Dreisig

Originally Posted by grey (Post 687733)

mine only comes in uneven terrain, low speed only, and is irregular. The noise only comes from front right side wheel. FunfDreisig, is this a known thing? what do you think it is? its very intermittent but it exists.

Originally Posted by FunfDreisig (Post 687388)

Does this only happen at low speed on uneven terrain? Is the knocking sound only a few 'irregular knocks' or is it several more 'rhythmic knocks'?

FWIW BMW techs are paid to replace obviously broken stuff quickly, not diagnose intermittent problems.

Funf Dreisig

Originally Posted by FunfDreisig (Post 687750)

I'm not sure about the E70 but we had a similar problem with our 2001 E53 that drove me nuts until I finally diagnosed and fixed it. If my X5 was still under warranty I would take it in to have the dealer do a thorough front end check for any worn/broken components. AND I would require them to remove/check the rubber frame mounts for the stabilizer bar, even if it meant I had to pay to have new rubber bushings installed in the 2 mounts. They don't cost much and it wouldn't hurt to have new ones anyway :)

Details:
One quirk of the X5 front end design is the large, flat, thick aluminum Stiffening Plate under the engine and the location of the front end Stabilizer bar (AKA roll bar). In the E53 the bolts that attach the stabilizer bar are the same bolts that attach the rear of the Stiffening Plate to the frame. This means that any noise created by the stabilizer bar is amplified by the stiffening plate/frame. Essestially the Stiffening plate acts as a speaker/megaphone making the sound louder. In the E70 the stabilizer goes in front of the engine; but I suspect the mounts are still close enough to the front of this large aluminum plate to allow the plate to amplify the sound.

In our E53 the stabilizer bar became crusted with road grime that built up between the bar and the rubber bushing in the mount. The grime was very rough and so crusty that it required a utility knife to scrape off the bar. This crusted on grime caused the stabilizer bar to 'grab' the rubber bushing and twist it inside the metal mount holder. After a little more twisting the rubber mount would slip back into place with a snap that was amplified by the stiffening plate.

This snapping can be forced to happen by driving very slowly over uneven surfaces in a gentle turn to get the stabilizer bar to twist. For example when pulling into or backing out of a garage or parking space where there is a 1-2" lip. Or simply over an irregular road surface. The trick to making it 'snap' is the get one front wheel higher/lower than the other three wheels at very low speeds so the stailizer bar has time to twist and release the rubber bushing in one large snap. If you go too fast, it still snaps but the snaps are much quicker and quieter. Think San Andreas Fault. You're going for the big one :yikes:

Funf Dreisig