Whoa, fellas - let's take a second to find out a few things. 88-toy: what engine are you running; is your truck exhausting through the factory pipes or upgraded system; describe the "winning noise" (I assume you mean "whining" noise); is it constant, or does it change in volume or pitch or both?
I you're running a Powerstroke diesel, the whining may simply be the sound of the turbocharger coming out of the rear pipe; this sound will be more pronounced if your exhaust was upgraded to a 4- or 5-inch system by the previous owner. If your whine begins as a low-frequency hum and gets higher with speed, it may be your rear end; however, if it is a low-frequency hum that stays low, or is heard mostly when you are accelerating or towing a load, you may have one or more bad U-joints in your drive shaft.
If you don't have much mechanical experience (things like eyeballing gearsets, straining or plugging for metal debris, reinstalling differential covers and refilling differentials with the appropriate fluid(s)), do NOT, under any circumstances, remove your rear differential cover just to have a look at the gears unless you have access to a mechanic who does house calls; if you don't, a tow to the shop of your choice will be in your immediate future. I'm sure Mark V is a knowledgable fellow (he IS, after all, a Moderator on this site), but if you don't know what you're looking for or what you're looking AT, pulling the diff cover is not going to do you any good, and will only render your truck temporarily undriveable. | 
