Sometimes all they want is some grease.
But a clacking from the back end, that increases with speed, is much more
worrisome for wheel bearings to me. I would want to find the problem before
the clacking turns to the high-pitched squeel that preceeds the locking up
(of either CV or bearing).
My bad CVs did clack on turns--but only between 20-35mph, mostly on mountain
roads, turning right. Turns are where the CVs are at their greatest
differential strain, unless you have a Syncro. If you haven't had them off
in 2 years or more, they would at least benefit from service and you can
spin the wheels to check the bearing with them off.