Does it have a one or two piece driveshaft? If it's a 2 piece, check out the carrier bearing and universal joint where the two shafts join. Also try jacking up one wheel at a time and run 4th. gear at 15 MPH or so on the speedometer while someome listens for noise at the hubs. Don't exceed about 20 MPH on the speedo, as the spider gears will spin the hub at double the speedometer reading.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!