So I finally got a chance to get under and look and I don't think it's the axle. The boot is in great condition and not any grease leaking out of it at either end. The boot on the tie rod does appear to be torn and there is grease coming out of it. Do you think that the tie rod could be causing the clicking? I took a few pics when I was underneath.

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2003 BMW X5 3.0i