2001 blazer started making a terrible grinding noise...I was told the noise was because the 4wd is trying to engage for some reason while I'm driving down the road when I haven't even used my 4wd for over a month. Can someone tell me why this would be happening???

 

First off,after having owned our '96 Blazer for over 10 yrs,I'm now a firm believer in engaging push button 4WD's at least once a month in order to keep the system in good shape.

You've got two parts to your 4WD system. The transfer case and the front axle engagement system. Which part were you told is suppose to be trying to engage? Where does the sound seem to be coming from? It's very possible that the vacuum switch on the transfer case is letting the actuator(under the battery)try to engage the front axle. Could be the switch or a problem with one or more of the 3 hoses that attach to it.

 

The noise seemed to be coming from the front...come to find out i had a broken vacuum line so that problem is fixed BUT now if I let off of the gas pedal too quick something underneath makes a terrible clunk ( i want to say it sounds and feels like the driveshaft is catching or stopping for a split second??? ) and also Im leaking fluid from the rear end at the rubber seal...hoping i didnt completely ruin something when I was having the engaging problem

 

I'm not so sure your problem is fixed. The system uses vacuum to activate the diaphragm under the battery. The diaphragm is sucked in, pulling on the cable to engage the axle. A bad vac hose will cause the system to NOT work at all.
I could be wrong, but it sounds like you have at least one worn out U-joint.

 

I can tell you with certainty that you need a new transfer case vacuum switch. Takes 5 minutes to replace.