Rear end noise at 45-50mph

Please help have a 2002 montana AWD with 70000 miles on it I have replaced most of the sensors and a really expensive rear end. GM is having a hard time figuring this one out. At about 45mph a loud whining noise emits from the rear end. When I first got it if the AWD system disabled it would stop the noise all together. After they changed the rear end it got better but now we have snow on the ground its getting worse. Im sick of spending money to try to find the problem any ideas?

Welcome to AF, realistically we cannot hear this noise, if in fact it is coming from the rear diff, take it back! Wheel bearings and unevenly worn tires can cause a noise similar to the differential.

the noise sounds similar to the AWD tring to engage or I have heard the sound in 4wd vehicals driving on dry pavement while 4wd is engaged. The high pitch whine that is coming from my montana goes away after 55mph and before 45mph but is very loud. There is no shake or shimmy it goes down the road perfect and they have replaces the hubs and bearings in there first try at it. I have worked on vehicals all my life but i'm not familiar with the new ones like this. I'm afraid that somthing expensive is wearing and I know GM doesnt care if it goes they then could dyagnosis corectly thanks for any help!!!

thanks for the feedback it seems though it has somthing to do with the AWD system once I disconnect the system it doent make the noise

When you do that you eliminate certain drive functions in the transfer case and the front drive shaft of course, so based on your description sounds like an issue with the t'case? If the shop drives the truck what do they say they think this is?

They thought it was one of the wheel sensors telling the transfer to somewhat engage the awd at the problem speeds but they changed all the sensors in the wheels and in the rear end after they put the new rear end in it thinking it might be the rear end. They are stumped now because no flag is being sent to the computer to indicate false sensor or reading. I know that there are several clutch plates in the awd system but if these were gone it would make the sound all the time right? and it should send a signal to the computer. The GM dealer were I have been taking it is stumped and seem to be trying differant things that cost alot of money. I will probebly try another dealer. Thanks you so much for your feedback and giving this some thought please anything will help this van has over 4000 dollars in parts and labor dumped into it and my wife and I love it just need to get this problem resolved. thanks again

I don't understand how a shop is putting this money into the truck then leaving you with a truck not repaired, I'd be back on their doorstep for a refund or a demand to fix it once and for all, this doesn't happen around here, s' would hit the fan!

I agree we bought this from a ford dealer and they had to send it to the GM dealer in another town. It was under warranty but it came down to them either making us take anouther van we didnt want for more money or taking our van and risking it. I think I might bring it back to them and do what you said and demand it be fixed thanks for all your feedback happy new year!!!