The 100-400 I dropped at the airshow came back from Canon. One thing I noticed is that while carrying the lens in my hand, I can feel something clanking around in it. When I engage the AF, this same thing goes clunk at first. Is this from the IS system's floating elements? I can't say it appears to have affected picture quality, which is once again damn good. (I even put a Kenko macro extender on it, and can't believe what I'm shooting.) Nevertheless, I'm concerned about the clink/clank inside; 'didn't notice this before at all.
Second, I found that on a monopod, this lens balances very poorly once you've stretched it out to 400. Simple physics there. So I tried taking the lens collar off and actually putting it around the barrel; the collar was a b---- to get off, and now something inside the collar that the screw fit into is rattling around, and I can't tighten the screw to get the collar back on!
If you don't want to rely on the IS always, does another manufacturer make a better-balancing collar guismo for this lens?