Jack the rear end up, and start rotating those rear wheels as fast as you can with the tranny in neutral. If you hear sound, disconnect the drive line and do it again. If it's gone, just buy new u-joints, ***** greasin em cuz they're really cheap and you'll have many years till you gotta worry bout em, though I'd still grease em occassionally after they're new cuz guarantee the previous owner(s) never did it for your current ones so who knows what happened there. Might just do it anyways. Greasable, strong, Ujoints for both drive lines are $60 from Napa and worth their weight in gold. Bearings were like $30 for the front and $60 for the rears (went for the sealed bearings on that one). When replacing bearings, or ujoints, always do both sides, i.e. left and right or front and rear.
If no sounds at all from the rear, jack up your front, and do the same to the front wheels. Try locking in one at a time as well. This should help identify if it's the front. If with the drive line connected and locked it makes sounds go for the ujoints. If not locked and it makes sounds, replace your bearings. They're easy! and grease em up really really good. Hand packing is a great way because typically you'll get a more thorough job. Pull the brake dust shield off too. I've found sand and rocks stuck in those vent holes and in between the shield and rotors causing terrible sounds, like banshees from ****.
If it looks to be the rear axle, those bearing **** to replace but it can be done. Inspect the gears of your diff and the oil from there too, make sure there are no shavings. Also might want to visually check your axle to make sure there is no sag to it, cuz it might be bent which will split your differential and carrier into all sorts of pieces in ttime. If you see any strange wear, chips, warping on the carrier or gears, you're definitely looking at a new diff.
If you buy a new axle, save your old axle shafts. I bought a new one and my rim got stuck on a center cap, had to beat the crap outta that thing with a 40lbs bar bell. Used the old ones and my axle works great. Don't automatically swap them out either, try the new ones and if the tires slide on easy, you're good to go.
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