Grinding

I have a 1994 Chevy full size blazer
An the other day i hear a grinding noise
coming from the floor shift that
ingauge the 4x4. When am in 4wd high
no grinding but when i shift back to
2wd an step on the gas its starts to
grind. Its sounds like when so eone
new learns to drive a standard for the
1st time an here is where I hear the
sound grinding from an can fell it as if
its wanting to engage