Re: noisy dana 18?
As said before, the idler shaft and its bearings usually get blamed. But, I would add to also take a good look at the 'end-plays'. The end-play of the idler gear is very important, and is controlled by replacable thrust washers. If the case is worn, you will need to make or find some shim-type washers to put behind the factory thrust washers. I've found that the end-play on the output shaft is a big contributor to noise. It's a shim adjustment, and I have found that I can not rely on 'feel'. I've got my best results using a dial indicator, and setting the end-play 'by-the-book'. I haven't had too much trouble making them as quiet as new, if I do it by-the-book.