Howling noise in drivetrain

[yogiTX]

I have a 1999 GMC Suburban 2WD. There is a loud howling or whining noise that seems to be coming from in between the driver and pass seats to me but others have said it sounds like it is coming from the rear? It only happens when my foot is on the gas. At 40mph it is very loud. I have changed out the tranny fluid, diff fluid in rearend and the u-joints. At this point I can't tell if it is from the rearend or the tranny area. Any help would be appreciated. Truck functions fine, no problem with shifting or torque, just the loud howling. Thanks, Randy

[Cableguy]

Unfortunately it sounds like rear end carrier and gears might be at fault. I hope I'm wrong....

[yogiTX]

Thanks Cableguy. How would a shop determine that? Is there a way I could verify it is the rear end? By the way, the suburban has 102,000 miles on it if that helps. I didn't see anything that looked out of place inside when I changed the diff fluid out but then again I don't know much about the axle. And yes I did add the limited slip addative from GM.

[Cableguy]

The time it happened to me I put truck on hoist with mechanic up there gently easing into it, so I could here where it was coming from. Then you can hear wether its a front/back ujoint, bearing or carrier or whatever. I have used axle stands and wheel chaulks on my hot rod truck to dial in gears that I changed. I was trying to set up gear messing after I went to 4.10's. But in your case you just want to hear where its coming from. Safety first! if your not comfortable go to a shop.