Clicking in front left tire when in 4WD...HELP!

Hello all. I have a 2001 Blazer 4x4 and all of a sudden one day it started making a noise in the front left wheel when we put it in 4wd. It sounds lile the hub is not engaged, and makes a noise as it tries to go in as the wheel rotates.

I looked on a few websites, and learned a bit about the vacuum actuator, and just finished checking that out. It seems to be working ok, does the 2001 have the vacuum switch on the transfer case as well? How do I know if that could be the problem? I hate paying mechanics to do things if I don't know what they are going to do.

Thanks in advance!!!!!!

sounds like a cv joint check youre cv boots any tares could mean dirt and mud got into the cv joint and messed it up so you will probley have to by a half axil

On an 89 the front axle half shafts turn all the time , they only get power when the diff is engaged . Is yours the same way ? If so then your wheel bearing may be a little loose and when you have power going to it instead of it just rolling it may be pulling against a surface otherwise not touched by freewheeling . Robert