When my hummer is in 4 high (regular drinking mode) it makes an awful grinding noise in reverse and drive. As soon as I put it in 4 high lock there is no noise in reverse or drive can someone please help explain this to me and what it might be.

 

From your description it seems like you have an issue inside your transfer case.

 

Whenever you ask a question, provide the year and model of your Hummer so you can actually get an answer.
Vehicle questions do not go in this section, they should be asked in the section designated for whatever the vehicle is..... for instance, H3 questions go in the....... wait for it....................................... H3 section.

 

I found out that I have a broken cv Axle and that's what was making all the noise when trying to shift into gears. The tale sign was all the grease thrown everywhere from the rubber boot and being able to wiggle the axle with my hand.