So I own a 1998 Chevrolet Blazer 4wd and my 4lo works fine to my knowledge but whenever I engage 4 high it makes this loud whining noise and today when I engaged it it did the noise immediately really loud and when I tried to put it back in 2 high the axles kind of stuck for a few seconds and then released what could be wrong with it

 

I'm having the same exact issue with my 98 Jimmy. When I change to 4hi it starts making a loud howling sound then when I go back to 2hi it doesn't change right away. I did find a leak in one of the lines coming from the vacuum switch but it did not fix the problem. I'm going to try replacing the vacuum switch and see what that does.