sounds like knocking in bottom of engine

Knock sensors do what their name says, they detect knocking; they don't cause it. Their purpose is to detect spark knock that you typically will not be able to hear.

A mechanic will have to listen to what this knock sounds like. Major engine problems aren't common with this engine unless the oil level got too low. The cause of that type of knock will result in the oil pressure warning light turning on. A vibration damper can break and cause a knocking sound too.