I think he should grab the cv shaft going into the wheel and shake it to see if there is any play. Even if there is the smallest amount of play, that would equate to a clunk sound while driving. And if he's not sure, he can just shake the cv shaft on the other wheel. If there is no play there but there is on the side in question, then you may of found your culprit.

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2000 X5 4.4i w/ 150K miles.