I just noticed a high pitch faint whistling noise coming from under my hood... Any ideas what it could be? Is this normal? I can barely hear it over the engine but its there...

 

I've read past posts that the windshield gasket can deteriorate and whistle, could it be the noise is comin from your windshield and not the engine compartment?
Maybe your Hummer has a Blower.

 

I dont think its the windshield.. I cant hear it when Im driving only when i'm parked and the engine is running I hear a whistle... blower?

 

A Blower you don't have. A blower is a turbo charger, forced induction.Some whistle and you certainly can hear it. I'm playing with the words, you know, Hummer/Blower.

Other than the widshield I've not read any other complaints about whistling. At idle, it could be a belt perhaps, but that is more of a squeal.
Next time you hear it, pop the hood and listen to where you can get an idea where it is coming from.Cooling system, front of the engine, side whatever.

 

Is the sound outside or inside? I noticed mine doing a high pitched sound the other night. At first it sounded like outside but when I opened the door it actually went away. I listened more and it was coming from fromunder the dash. This was while not moving, then I noticed it there whiledriving this morning too. When I changed the vent settingit went away. There are 2 positions that the air dirverteristurning intoa reed and playing music forme. I'll swing by the dealership this weekend and see if that is something they can quickly correct.

 

My whistling is coming from under the hood... I cant pinpoint the location thou... [&o]