Just got mine today and it has the clicking noise as well. It must be by design.
Since the earlier copies didn't click, you're suggesting that Canon intentionally made a design change during production that resulted in this clicking noise?
its not that big of a deal though
Noise results from friction. Friction causes wear. Maybe it's not a big deal today...but since wear is cumulative and lenses have a (potential) lifespan of many years, I wouldn't be so confident that it's not a big deal...
If I bought a lens that clicked like these recent units do, I'd return/exchange it.
Now, maybe it is normal - the 300/4L IS makes a loud 'clunk' when the IS kicks in, and then the operation settles down to a low growl. But the thing I find troublesome about the 24-70/2.8L II clicking issue is that it appears to affect only more recent copies, and not all of them. That suggests a manufacturing problem, not a design change.