Computers should generally not be making loud noises, such as grinding or rattling noises. It usually will just make a low hum noise.
Rattling may indicate loose components. Scraping noise may indicate issues with the hard drive. Clicking noises may indicate hard drive or fan issues. A loud pop could indicate a blown capacitor. This may be accompanied by the smell of smoke. The top of a capacitor should be flat. If you see any that are bulged or missing the outside completely, then it’s time to replace those components.