I have a 2002 blazer 4x4 that over 25 mph there is a whining noise like a bearing or gear. I changed the front bearings back in November because one was bad. I checked the oil in the front differential and there is no play in the front bearings or the cv shaft. The noise doesn't change if it is in 2 or 4 wheel drive, also it seems the same on turns and goes away under 20 mph. It started about 3 weeks ago and seems to be getting louder. Im running out of things to look for so any help would be appreciated.

 

Have you made sure that when you are in 4wd, that the front wheels are actually powered? It sounds like the engagement collar is stuck...

Do you have a 3-button or 4-button 4wd switch?

 

It has the three button setup for the 4wd. I took it to a snow covered parking lot and tried 2wd and the rear wheels spun then tried the 4wd. It did engage the 4wd and the front tires spun. I am starting to wonder if i got a bad front wheel bearing when I replaced them a few months ago. Does the front drive shaft turn when it is in 2wd? That u joint is the original 64,000 miles on it.

 

With the NV233 transfer case, your driveshaft should be free to rotate when in 2wd (ie not powered).