Lots of noise on start up?

[ctupton]

Hey guys need help on something... My Hummer makes lots of noise on start up. Sounds like a jet taking off and I was told this is a normal hummer sound that they make when they are warming up, and the noise will go a way after a few minutes of driving... well I can drive to work and it will still be on, whatever it is zaps the power as well. To me sounds like a cooling fan and usually if I floor it or put in neutral and floor it will engage and silence. But none the less it is annoying that it can go 15 miles in heavy traffic and not turn off. When I asked the dealership when I went back to pick up hats.. they said it was normal and that it is part of the 4x4 system but shouldn't make the noise more than a couple hundred yards.

Help!

Also I think it is kicking the crap out of my gas mileage as well, 156 miles on half a tank and that is mostly highway, not sure how exact the half tank is mark is vs how much gas is really in there.