What would cause noise from the engine on a 2000 Toyota Camry?

Different problems cause different noises. A squealing noise may be coming from th ebelts. A hissing sound may be the result of a vacuum leak. A tapping metal sound may mean you have a lifter stuck. Try to isolate the noise, find out if it is from front, back, top, bottom or which side of engine. Try to describe the area it is comign from, and what it sounds like. With all the moving parts being comprised of so many different materials, it is impossible to answer this without some clues and better description