While shooting this weekend with my 20D and 300mm F/4L, I noticed there is a slight amount of play between the lens and the body. It's barely enough to be noticable, but loud enough that if I rock it back and forth I can actually hear it. The play seems to be in the rotation of the lens on the body.
I also just tried my kit lens and the 50mm, and they both have a little play in them as well, but are not as audible as the 300mm, probably because of the size and weight of the lenses.
Is this normal, or something that can be adjusted out somehow?

