One thing I have found with the diffs I have done while at the dealer is that if the howl-whine has been present for an amount of time due to bad pinion or side brgs, replacing the brgs will have, at most instances, no effect because of a new gear pattern being formed because of the bad brgs.
 My Rag howls, my fault as I let the oil go too low when I had a leak back in the late '80's, and it still does it to this day! Just remember, a whine not growl, is caused by an incorrect pattern! This also happened to me in an '80's p/u that the guy let go too long as well. The pattern was correct but no matter what I did, no change!! A T/A came in with a blown diff, 3 sets of new GM gears later, I had a good set, a lot of time spent on this one that still burns me to this day!
 If this is not the case, have you done a gear pattern test after you put it together? This is done using gear marking compound of white lithium grease if you don't have the proper compound. (Canadian P/N 10953497,GM compound is yellow) You will have to rip it apart again, remove all oil from the gears and using the compound, set the diff via the pinion gear or case brg shims. I included these pics as well, hope it helps!!!!!!!!!
 

-- Edited by 67Poncho at 11:39, 2008-10-12

-- Edited by 67Poncho at 13:02, 2008-10-12

yes i did

Are you using GM gears and did they have any signs of wear or rust on them?
Does it howl all the time or only at some speeds?
 Some gear sets available aftermarket howl no matter what you do.