If the engine has a knocking sound like someone hitting something with a hammer then it could be a rod bearing. It is best to have it looked at right away. It may require a complete engine rebuild.
your engine is loud because, the fan makes that noise
The cooling fan is coming on cooling the engine. Very normal.
Exhause leak? Bad Muffler? Leaking or cracked exhaust manifold? Bad EGR valve?
If the 1999 Suburban noise is a sort of loud banging noise, the problem could be that the engine have jumped time. Jumping time would cause the noise and jerking in the engine.
The fuel in the cylinders exploding
Take it to a repair shop and get it fixed!
Check your catalytic converter.
i have a very loud tapping noise in my BMW 318i e36 1993 engine. its extremly loud on start up then drops down to very loud when idling. the noise never goes away. I've had people say the engine was about to throw a piston, i need a new engine, etc what could it be and is it possible to fix?
Muffler
You have to locate the source of the noise then repost your findings.
Yes, a tornado is loud because of the high winds swirling around it, which can produce a loud roaring sound. The noise is often compared to that of a freight train or jet engine.
Loud engine noise is usually a result of a hole or disconnection in the exhaust manifold or muffler.