In article <4hce79$n7t@news.NetVision.net.il>, itamar_e@plato.tau.ac.il says...

>Today to my surprise I found up that the rear lens group of
>my Nikkor AF 70-210 f4.0 zoom lens became released. After screwing
>back the lens group to its place carefully using my fingertips,
>I noticed that when I'm shaking the lens it makes some noise and
>the front part of it (the one that rotates in while focusing)
>rattles a bit. When I hold the front end of the lens and shake it
>I can still hear some noise.
>Is it normal behaviour of this lens or should I send this lens for
>service.

Since vibration from some source (plane, car, or....>motorcycle?!)
has caused the one loosening on the lens, I would worry about more.
But, AF tele zooms do have floppy front-focus sections (part of the
exquisite inelegance of AF lens physicallity...;-), and internal
mechanical parts that rattle. Check the lens over for obviously
loose parts, tighten them, if possible, and proceed to use the lens
until something actually falls off again. Protect photo gear from
vibration as best you can. If it ain't broke, avoid those expensive-and-occasionally-disasterous CLA's.....
Hope This Helps