A common problem with noises is that the customer assumes the noise is obvious and there for should be no problem to fix. The truth is that if you have a noise problem the best thing you can do to ensure everyone (especially the technician) is reading off of the same page, is have the technician that will be repairing your car present when you demonstrate the noise. I can't count the number of times I've fixed a noise only to have the customer pick up the car and be rather upset because the "Noise" was still there. It has to be a real time demonstration to the repair technician, telling the service advisor about a noise, even being very discriptive, usually doesn't work.

Now that I've shared that

When you first start your car and it is cold, there is an airpump that will run for a while when you start the car, it has often been discribed as a humming noise. In the morning when the car is cold, raise your hood and start the car, listen just below the battery tray and see if that is the noise you are concerned about, if thats the noise its normal. If that is not the noise I would suggest scheduling and appointment, and let the advisor know you want to demonstrate the noise to a Repair Technician, not the GM, not the Service Manager, Not the Shop Foreman (unless he is going to fix it), the repair technician. There is more than likely a nicer softer way to say the above, but problem like yours are one of my biggest complaints where I work, I really want to fix the car and can't do it sometimes unless I get all the facts.(especially noise problems)