There must be something that is off to give you a noticable howl. Did you perform the break-in on jackstands during the initial installation? This procedure will put the rear of the truck in the air and your run the truck in its highest gear at idle for 15 minutes. If you have an extra helper, have them get behind the truck and listen for gear whine.
Did you use a dial indicator to ensure the lash was correct? I have done three sets of gears and an increase in noise means something isnt right.
I have pretty much a step by step album on my Webshots page, feel free to check it out, the link is below......
