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Guy, from what I can tell this is a common problem with some earlier models -- I experienced the same thing with my 200-400VRI and 200/2. The squeaking wasn't continuous and often occurred after sitting for a while...giving the impression that it is "lubricant" oriented.
Bottom line is that both lenses were sent in to Nikon Canada for servicing, specifically for the "squeaking" issue, and both were returned with a clean bill of health...and they still squeaked.
Whether Nikon simply didn't want to replace the AF-S motor or whether there really isn't a problem, I can't say. I used them for a while with no issues but eventually sold both.
From my research on the issue, what I think is that in most cases the squeaking isn't a sign of imminent failure unless perhaps it starts to squeak continuously. I suspect Nikon knows exactly what the problem is and quietly made a mid-model change in the AF-S assembly, but of course we'll never hear about it.
Bottom line is I wouldn't worry about it unless it starts occurring more frequently.