At 2000rpm and above a buzzing/humming noise is heard. on 2007 Ford Ranger

This noise sounds like a bearing that needs to change but I already changed all the bearings in the van. Have been told by three different repair shops that the turbo is going through. But there have been no signs as mentioned on the internet about the turbo. I'm still able to build great speed and no black blue or white smoke. Not even regular diesel smoke seen. I have taken all the precautions to prevent the black diesel smoke. Please advise as a turbo for the Ford Ranger Thunder is very costly.

Asked by for the 2007 Ford Ranger
have competent technician look at it