Mech says "Rear axle needs shims", huh??

Has anyone run into something where their mech says the rear axle needs shimming? I took my 5'er into the dealer 3 months ago for a 4-wheel alignment, he said nothing. Now I'm trying out a new mech much closer to my house (lot of bmw's in his lot) and he reports that the rear axle is "off", camber I think he said.

What he described was to take off the rear assy on the driver's side (drum, brakes, all that stuff) so he could slide in shims. This just seems odd is all.

Anything else he noted I was already aware of (i.e. front struts, inspection light, etc.) to his credit I'd say.