Replace the bushings on your front control arms. i bet that's your problem.
Does it happen a little more if you're turning on the highway? like long sweeping turns at 140-150 km/h+ starts rattling like crazy?
Take it to your mechanic (i suggest RMP, mirek would suggest Bimmersport)
Replacing the bushings on front control arms isn't too expensive, and i know RMP has a press to pop the bushings into the control arms.
For a quote, call 905 951 0002 and ask for rocco
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