knock?

well, if you are referring to spark knock, or ping, or if you are English, pink, this refers to when the piston is travelling upwards on the compression stroke and something (a hot spot, too much boost, too low an octane fuel etc) causes the mixture to ignite. but the piston is still moving upwards with great force, and should not be going down yet. also, the spark plug has not fired yet and when it does, the flame fronts will collide, causing the noise you hear.

the nasty forces created by these uncontrolled flame fronts at the incorrect time can cause mild to severe damage, and is to be avoided.

on low compression, normal street engines, especially modern engines, as long as they are normally aspirated (no turbo or superchargers) this is usually not an issue and it has to be pretty bad to damage the car. If your car is very high compression or has forced induction, it can be a very serious issue.

In DSM's and other cars, the computer will sense knock and retard the hell out of your timing. you will loose tons of power but your car will probably live thru it.

you need to diagnose why you are getting it and fix it.