hey guys, i have a 97 4x4 blazer and i got in it yesterday and took off and a few minutes down the hwy, i get this roaring noise. it sounds kinda like the front end of the truck is where its coming from. i get to where im going and when i leave the noise comes back a few mins after i get rolling down the rd. i pullled off on a side road and put the 4x4 high on and the noise goes away. i drop back down to 2 wheel and the noise comes back? any ideas? im a newbie when it comes to anything car related so hopefully u guys can help .
thanks

 

The front axle is not fully disengaging inside. There is a lot of information about this on the forum.

This thread should cover things sufficiently:
4wd Front Axle Clicking When in 2HI - Goes Away when in 4HI/4LO