I have a 1989 Chevy S10 Blazer and it snowed pretty good for Upstate S.C. and I had to put it into 4 wheel drive, but now the front end is making this kinda grinding sound and I have no idea what it is? It's kinda off and on while you're driving...like, grind...grind...grind...grind, but as soon as you touch the brake pedal it stops. Please help me!!

 

Does the noise go away if you put it back in 2wd? If so, you likely have a problem with the front axle engagement system. The link below covers this system fairly well and is applicable to just about all of the s-series 4wd trucks just don't let the thread name fool you.
4wd Front Axle Clicking When in 2HI - Goes Away when in 4HI/4LO