howling in rear end

I have a 2004 Astro AWD. It has a howling in the rear. It starts about 15mph when under load but goes away when costing. It varies is directly linked to speed and not affected by RPM or what gear I am in. I also noticed that at lower speed (10-20 mph), if I break hard. the noise is there. Any ideas.

I have a 2004 Astro AWD. It has a howling in the rear. It starts about 15mph when under load but goes away when costing. It varies is directly linked to speed and not affected by RPM or what gear I am in. I also noticed that at lower speed (10-20 mph), if I break hard. the noise is there. Any ideas.

http://www.differentials.com/diagnose.html

As the link says you need to check the ion bearings.
Let us know what you find.