Why does my Toyota Corolla's engine make a knocking sound?

I recently purchased a used Toyota Corolla and noticed that the engine makes a knocking sound when I turn it on. Is this something I should be concerned about? How can I fix it?

It is possible that the knocking sound is due to low oil levels or dirty oil. Try checking the oil level and changing the oil if necessary to see if that resolves the issue.

Another possible cause of the knocking sound could be worn out spark plugs. Consider replacing them to see if that eliminates the noise.

If the knocking sound persists, it could be a sign of a more serious engine issue. It's best to take your Corolla to a mechanic for a thorough inspection.