Hummer H2 2008.

My front end makes a tinny sound when i first start my truck. Happens a few times while truck is warming up. Also, If I am in park, and I push brake pedal all the way down I can replicate this tinny sound. It lasts for about 5 seconds.
Doesn't happen when Im driving and braking. Not sure what it could be since noise is happening without truck being in Drive or moving. Anyone have any ideas?

 

Loose or cracked exhaust shield would be a good place to start, belt tensioner/idler pulley would be next on the list.

 

Just hard telling without being there to hear and even then it can be very hard to track down noises. I've got one that sounds like a low chirping sort of sound from what sounds like behind the dash. Only hear it in gear at a stop. Still have not been able to track it down. Have a couple others as well. Quite annoying.