* What kind of engine are you talking about? A car engine, a motorcycle engine, a plane engine, or something else?
* What is the specific sound like? Is it a high-pitched whine, a deep rumble, a knocking sound, or something else?
* When is the engine loud? Is it always loud, only when accelerating, or only when idling?
* What is the engine's condition? Has it been recently serviced, or is it old and worn down?
Once you give me more information, I can help you figure out why the engine is so loud.
