I have a 2000 blazer and have the grinding noise at 50 mph and higher. I can feel it in the drivers seat. I have replaced the entire rear axle and the front hubs. Still got the problem. I talked with a guy that works on Blazers and Jimmys all the time. He told me to replace the front differential, he says after 150K miles the outside bearings go bad and it is a lot cheaper to replace it with a low miles differential. Just make sure if you do, to check the G code in the glove box to make sure you replace it with the same G code. This will keep the ratios the same.
I am going to replace my front differential soon and will post the out come. This site is great, and has helped me keep my Blazer running good.
Thanks
Jack C.

 

Seems like a lot of work every time your front wheel bearings go bad. And it isn't always cheaper. If you get your wheel hub/bearing assembly off of eBay from a company called Dearborn Axle, it is cheaper than everybody else.