I have a 10-year old 70-300mm 4.5 - 5.6 that has, for a few years, had a bit of a buzz in the focus ring. If you turn off AF (or unmount the lens) and spin the focus ring, it sounds a lot like the "resistance" on a fishing reel (only less high-pitched). Or for those of you who didn't grow up fishing, maybe something like a fingernail dragging gently on a ridged, plastic surface like a plastic file folder. Sound can almost be eliminated if you turn the focus ring slowly, but gets much louder if you spin it from one end of the range to the other quickly.
I know the analogies are bad, but bear with me -
I never worried about it much because I almost never use the lens. Only reason I give it another thought is if I wanted to sell the lens (meh).
But now my 50mm 1.8D is starting to do the same thing, and I use that one a lot. Lots of google searching just turned people ranting about how much quieter AF-S lenses are than AF-D ones (again, meh). Anyone ever heard anything like this before? Definitely didn't do it when they were young, but a couple of years later, started to. AF works fine, manual focus works fine (though not QUITE as smooth). Don't want to harm the focus motor on my D600, so got really curious when the 50 started acting up. At $125 to buy a new one, I'm obviously hesitant to just ask to have it repaired. But if something like a cleaning would make it go away, I'd do that for both lenses without hesitation.
I can swing by my local Calumet Photo (or similar) to ask them, but thought I'd post it here, just in case it sounded familiar to anyone.