One of my CVJ-rebuilt axles did that for a thousand miles when it was new but suddenly stopped and has not returned. CVJ said not to worry about it and I'm not.

If your boots aren't torn and leaking, it may be that one of the balls in the linkage has slipped out of position and is getting knocked around by the fingers of the joint. I know from my experience that you can hear the clicking just fine at highway speeds, even over the engine noise of a 617.

Unlikely to be the differential making that kind of a noise. You could drain the oil and see if it has metal in it, just to be on the safe side. Refill with any good 85-90 weight gear lube or Mobil-1 synthetic if you want to get fancy. Remember to remove the fill plug first!

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970