Need help i have a 2006 hummer h3 with 5 cyl engine base package 110000 miles on it when i accelirate fast and uphill makes gear grinding noise like clack clack clack then goes away seams like its coming from the transfer case please help diagnostic

 

When was the last time you changed the Transfer Case fluid, front diff lube, rear diff lube? Your description, may we assume you are driving on pavement if Hi and not on Hi Lock?

 

I wouldn't call a "clack" a grinding noise. Uphill - what kind of angle does it take to do this?

Are all the front axle bushings good?

 

If you hear a "clack-clack" kind of rattle it could be a sign of piston slap.

 

I have personally seen an 06 do that when under load wheeling uphill........... the clack clack clack thing.

Owner suspected worn out T Case chain, too slack and skipping. If I remember right, it was the old plastic T Case Fork not holding lock 100%. Could still happen on pavement if popping in/out of lock or close enough to make the racket?

 

How did you SEE a "clack clack clack thing"?

 

Poor choice of words....... "observed" as in saw it for myself. That would be use of the eyes while the event was occurring to note that the 06 H3 was under load climbing a hill and use of my hearing to discern the clack clack clack thing at that time.

 

Yet, under a load, you could get a piston slap: "clack clack clack thing". OP needs to check where the noise is coming from!