Mysterious high pitched sound can't figure out need help

Hi folks, i bought a 2005 chevy crew cab new from dealer ship and love it. about 2 months later i noticed a sound. At first i kept thinking someone kept honking at me until i figured that it was my truck making the sound. It can't be heard with the stereo on so at first i hardly ever heard it until i had my window down and started to pay attention when i would hear this sound. I seems like it is either coming from the rear end or transmission and usually happens when started out at a stop light and taking a turn, somtimes i nottice it when i change lanes while accelerating. either between 1st and 2nd gear or 2nd and 3rd. The best i can decribe this noise is it sounds like a car horn but not so loud, or an electric buzz. Like i said for a while i thought someone was honking at me. I have brought the truck into the dealer ship and had the shop manager ride with me and was able to get the truck to make the sound. He said he had never heard anything like it and would check it out. However they never found anything wrong. I'm not possitive they even looked at it heh. I was told the took it for a test drive and it never made a sound so they didn't pull the diferental off, probally didn't even pull a tire off. Anyways i'm still stuck with this mysterious sound. Has anyone had this problem or heard of anyone having a sound like this? Any help would be grateful and thanks in advance!