My Mac is making strange sounds?

My iMac computer is making a very strange noise. It sounds like a very loud static noise. When I attempt to turn it on it always makes this noise and the screen wont turn on. It’s done this once before and a computer tech looked at it but we couldn’t find what do. We threw it out and bought this new one. Is there anyway to fix it? Or even just save the information on the harddrive?