I hear bells ring when I boot my macbook pro up…but if you’re referring to like a weird sound that comes from the optical drive area / hard drive area, it’s like a weird clicking noise as if it’s engaging. If you had a disc inside the drive, it might keep trying to engage it upon boot up, as well as while your using it. Are you too far away from the router? Is the router maybe too old and not sending a strong enough signal, and cutting out from time to time? Can you stay connected to other networks just fine or do you have these problems everywhere? Have you tried hard wiring it to the router? I would take it to a genius bar, but there are a few things you can do to try and rule other factors out before making the trip.