My laptop is making very loud sound when I start it

Your description isn't very descriptive. The best help will come when you give us plenty of details like the model of laptop, what it or you were doing prior to the problem, has it had a fall recently.

If it has a CD/DVD drive, does it have a disc in the drive?

If it is more like the rapid sound of something caught or rubbing on your internal cooler fan, you will need to open the bottom of the laptop to get to the fan.