CLONKING/KNOCKING when accelerating, or taking of

Have you checked the bolts into the end of the drive shaft (14mm head under the dust cap in the centre of the hub) these have a habit of coming loose. Some people describe it as a crunch when setting off, accellerating and decellerating, on mine it's more of a knock. Tightenning these bolts gets rid of it for a few miles then they come loose again. They usually need stud locking back in. (or evidently replacing with xc90 bolts that lock somehow?) Be carefull if you do try to tighten them as they are fairly small and if you shear the heads off you're in trouble!! Can anyone with Vadis confirm the torque settings for these bolts or does it not give that sort of info? also can anyone confirm if the bolts on the XC are actually different (self locking) as my local specialist says they are not but I have read on here before that they are.