Get another mechanic, the most common cause is boot failure, there is a rubber boot over the CV joint and it is to keep water and debris out of the joint, If the boot is okay, the other thing to check are all the bearings to see if they have worn out and are allowing the shafts to wobble, If the suspension has been altered in anyway then the angle on the joints might be to much for the joint to handle.
Answers & Comments
Get another mechanic, the most common cause is boot failure, there is a rubber boot over the CV joint and it is to keep water and debris out of the joint, If the boot is okay, the other thing to check are all the bearings to see if they have worn out and are allowing the shafts to wobble, If the suspension has been altered in anyway then the angle on the joints might be to much for the joint to handle.