Do I need to send my lens in for service?

[Agilulfo]

As the lens functions flawlessly it isn't something I intend to get too worried about.

I think jrw is right.

In four Canon lenses (with and without IS) I can hear a slight sound when I tilted them, that can be described as "shifting weight". The more focal length, the more noticeable is the sound. As in a manual focus lens I've checked there is no sound, I guess there must be something related to the autofocus system.