pull the shaft out, cut the boot off and check it out, could be worn out, from memory there is a big clip that holds the shaft cup thingo (and big ball bearings) in there, lever the clip out with a flat-head screwdriver and it will just slide apart, do it on a workbench as the balls will just drop out, once you get it apart it will be easier to see if its worn past servicing, if its still in ok condition just get a new cv boot from veal for about $12 and it comes with cv clips & cv grease