the vent hose! out of the top where it hooks up to the bottom of the bed to vent! Anyone no why?? Im about to change the gear oil anyways. I got the synthetic oil from walmart for 9$ a quart and the friction modifier at the dealer for 4$ So i cost me 34$ to do everything!!

 

ya you either have to much oil in it or your getting the rearend to hot and boiling the gear oil and its coming out the vent tube