rearend problem

guys i need some advice.
my brotherinlaw has a 97 chevy 4x4 pickup.developed a whine in rearend.was told bearings were bad. had the three bearings replaced.sounded good for about 600 miles then whine came back.now there is another sound also.he said sounds like the whoop sound a bad tire would make.the tires are in good shape.seen a post about pinion shaft problems on these trucks was wondering if new sound could be pinion shaft or that could have been problem to start with.any help would be appericated

thanks charles