Tires: tire diameter on 05JGC, tire diameter, awd system

Question
I have an 05 JGC that makes a noise when backing up.  The dealer says its becasue the tires are not the same size.  I had a blow out on the rear two months ago and put on the full size spare.  The car only has 18K on it.  I bouught it used from the dealer 6 months ago so I don't know if the tires were rotated.  I was told that if there is 2/10ths of an inch height difference, it could cause a problem with the AWD system.  So does this mean if you have a blow out, you need to buy 4 new tires to make sure that they are the same size?

Answer
Dennis,

What this means is that you have to pay more attention to your tires and plan ahead.

Since you have a full size spare, it ought to be included in the rotation procedure so if you have a situation where you lose one tire in the set, you still have 4.

One of the alternatives is to have a new tire shaved so that it is the same as the others.