2004 z66 rear end whining

I am a new member but have searched the site alot before becoming a member. I am seeing a lot of chatter about rear end noise, so let me add my problem. 2004 Z66 291K, 3.73 rear end was rebuilt about three years ago (new ring and pinion, pinion bearing, carrier bearings and wheel bearings) about a year ago I started hearing a whining noise coming at about 50 to 60 mph when I step on the accelerator and it goes away when I take my foot off the accelerator  and coast. I have tried multiple things that needed to be changed anyways,  like new tires, new brakes and new u joints no help. The only thing I can think of might be the rear end work done 3 years ago wasn't done properly. Maybe installed bad bearings or incorrect backlash. I don't want to tear into the rear end again but it sounds like that is what may  be needed. Any help would be great thank you
DJ

Have you modified it with a lift and bigger tires ?

I would say one of your carrier bearings are likely bad. The place that did it for you before probably didn't do it right. I have the same problem with mine right now. What kind of warranty did you get? Take it back to them and see what they say. If they don't give you a break on it then I would take it somewhere else. Apparently whomever did the job didn't do it right. Mine has a lifetime warranty on it but I don't think my truck will make it to detroit and I don't care to leave it for a week so I am just going to install a hummer H2 rear and call it a day. That is a 3/4 ton rear end...

Rodney

No mods, no bigger tires

No warranty on the work. It's been over 3 years. I am thinking of going to another shop but thought I would ask the group. Thanks for your inputs.