I've done several searches and haven't found an exact description, forgive me if I'm duplicating a thread. 2007 H3, automatic tranny. Strange noise, kind of a whining, maybe even slight grinding but not a harsh grinding sound only when I engage any gear even though not moving. Put it in park or nuetral gets quiet, only starts when engaged. Going down the road it's kind of a high pitch whine and gets better as rpm's back off.... No shifting issues/popping noises/slipping, no idiot lights come on. Changed Transfer Case oil just to make sure, it wasn't low, dirty maybe so new fluid should only help but didn't take noise away. Tranny still feels strong..... thought mabye differentials or axles etc... but does it even sitting still with brakes on, and only when put into gear. Hope that description is good enough. Other than this I've had no issues with this vehicle, been a pleasure to drive for last 3 years... has about 73k on it now. Any help greatly appreciated!

 

Mine is doing this as well, I inflated the tires to the proper level, that seemed to help some. I wonder if it's something with the throttle body control

 

My front differential was making a whining noise and had a slight grind when I was stopping and taking off.

 

http://www.ownersite.com/tsb/tsbs.cfm/2009/HUMMER/H3/

Finally found this, Link above mentions a Technical Service Bulletin, referring to a bearing that goes bad in the torque converter. Guess replacing the converter is next move. Sux...but is what it is.