Glossary of Terms: Clonk
WARNING: This page is about a different car, the 2003 Ford Pickup, 2003 Ford F550 Super Duty, 2003 Ford F450 Super Duty, and 2003 Ford Excursion. However, it is still accessible from the selected car via links, so may be relevant.
A hydraulic knocking sound. Sound occurs with air pockets in a hydraulic system. Also described as hammering.