Transfer case making loud noise!!!!!!

Hey guys im wondering i have a 1996 chevy blazer and i have all-wheel drive not the push button 4x4....now when i got the truck i heard some noise from the transfer case found a bad u-joint on the tranfer shaft...replaced it..but i still get a very loud BANG out of it when i drive...and im wondering if there is a less expenive way to get the transfer case off or if anyone knows where i can get like cross section of the transmisson..cuz i realy dont want to rebuild the whole thing i mean it shifts fine no slipping just that loud bang sound...im thinkin the chain in the transfer case is bad so any help would be much apprecated..