A customer just came to the shop with a 1987 Blazer that he installed a 6 inch Pro comp lift. The Blazer was being upgraded to a 12 bolt and 3:73 gears at the shop. After installing the lift the truck makes a load rattle almost grind noise from the rear when decelerating. All u-joints are new and angles are not bad. The Blazer has minimal drive shaft vibration when on the gas and the noise dosen't come with a vibration. The noise was the same with the original 3:08 10 bolt and the new 3:73 12 bolt. I think the slip shaft is to far out of the 208 transfer case and when not loaded is rattling around from loss of support. I have never installed a lift this high in a Blazer and not changed the transfercase to a 205. And I have never had this problem with lifts this high with a fixed yoke transfer case. Would a fixed yoke conversion solve this problem or a longer driveshaft help. Please post your fixes, before I spend the customers money on exspensive parts that may not work.