X5 PROBLEM(Knocking sound)

[xrwrx]

Hi all X5 fans,

i have a 2007 X5 E70 with sports package,
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.

i took it to the BMW service center for like 5 times. frist few times.. the advisior told me dat they can t hear anything..everytime i left the car there for e whole day..till last time ..they get their Head person in charge to test drive with me.. then he heard the noise..
i was told that sometime losen..and they fixed it.
when i drove home..the problem is still there

anyone has similar problem ??