One time a member installed a 600 Griz axle in a newer Griz. Those old style double bearing and seal axles have a axle bearing race length about 3/8 " longer. Which meant that the hub could not be tighten up against the bearing. His wheels were loose and wobbling.
We first need to know which bike this guy has?
If it's a 660 Grizzly, we need to know which one as there is 2 different axles. A 2002 model or a 2003-2008 model? Did he install the incorrect axle? If he has a newer model, has someone installed the 2002 hubs and knuckles on it? If it's a 2002 model, has someone installed the newer axles/hubs in it?
What was the installation procedures used? Was the axle nut torqued properly?
Was the ball joints installed properly into the knuckle?