I had replaced a vac line going all the way back to the transfer case. I had pulled out a rubber connector atthe T case , it was a 3 port rubber with the vac line pushed into it. I was on my back in the gravel so didn't have much room but I managed to get it back on seemed to wok fine. but a day or two later I was driving down a highway and suddenly heard a loud vibrating sound, pulled over and couldn't see anything wrong. Sound was gone when I pulled away ?!? It happened a few times and couldn't figure it out. one time it happened a few K before a trail so I led it rattle till I got there and when I engaged the 4x4 the sound stopped. what the ?!? it took a bit to figure out that I had put the 3way rubber connector on 1/3 turn out and the vibrating sound was the 4x4 trying to engage without proper vacuum pressure. looking closely at the rubber connector (cleaning it...) you can see the key way that makes it fit properly. works fine now...