2005 GMC Sierra Crew Cab 1500 5.3

When turning the key I get a humming noise in the cab. There's a "speaker like" thing on the drivers side above and to the left above the head in the head liner. The hum seems to come from that. What is it?

Also when turning the key you get a grinding noise from the instrument panel which goes away at start up. Any thoughts on that?

I have a 2008 extended cab and noticed the same thing. I thought it was ambient radio noise, but it did not go away when the radio was turned off. I finally noticed where it was coming from and it almost sounds like a small fan. I moistened my fingers and put them over that little grill and it feels like it is sucking air into it. I then thought it might be associated with the climate control system in that is where it pulls in compartment air to measure its temperature. I looked in the owner's manual, but cannot find a reference to it.