diff or wheel bearings... how to diagnose?

[dutch]

my friend owns a 96 b2500 van.  The rear makes whining sounds, but I`m not sure how to determine if the problem is in the diff or in the wheel bearings.
what to do before ordering parts... 

[blknout]

you can use a mechanics stethescope and jack the vehicle up and listen for the noise.

[dutch]

   sounds like a plan....     I do wonder if things will whine when not under load.   I am pretty sure it`s the diff, but I really want to make sure... it`s not like you pick up a rear end for $50 down here   

[72cudamaan]

Drive the van in circles. If the noise disappears in either direction it's a wheel bearing.

[dutch]

thanks guys 

[dodj]

Drive the van in circles. If the noise disappears in either direction it's a wheel bearing.