Jake the Snake

Hey guys, I am new to the MTB forum and need a little help with my rear Elixir CR. I bought a 2010 Specialized Epic 29er Comp last Memorial Day weekend and it came with the Elixir R's. The noise and the drag on the rear wheel made me take the bike to the LBS and Avid warranty upgraded me to the CR's. So now I have no resistance when I pull the rear brake lever, it goes all the way to the grip. I have tried bleeding the rear brake about 5 times and I always pull out a good bit of air bubbles. So, there is an air leak somewhere and I was wondering if anyone had any suggestions as to how to trouble shoot the leak before I haul the bike back to the shop.