Engine knocking noise when idling?

Hello,

An engine can make that noise if it is simply low on oil. So first check the oil and make sure it is at correct level.
It can also make this noise it the oil pump is unable to provide sufficient pressure at idle. As this will make the oil not reach the upper part of the engine and it will make noise.

Here is a helpful article that covers the basics:

https://www.2carpros.com/articles/engine-noises

If the oil level is correct check the oil pressure. You can use a pressure tester to do this task. These testers can be rented from your local auto parts store.
This engine should have 60 PSI of oil pressure at 1,850 RPMs.

https://www.2carpros.com/articles/high-or-low-engine-oil-pressure

I have attached diagrams for your reference.

Please let me know of any questions.
Thank you.