Why is there a Knocking in engine

Knocking is never good! Is the check engine light or service engine soon light on? If so, you may have a bad knock sensor that needs replacing. You can try a higher octane fuel. But with today's computer controlled engines that shouldn't be a factor unless you're required to use premium gasoline. If this is a high mileage vehicle it's most likely worn bearings. Oil pressure problems are another sign of worn bearings. If you have both these things going on it's time to start shopping for a new vehicle or a new engine. A knocking engine is often very near the end of its life. Hope that helps! Jim