Knocking noise from engine compartment.

[deagz]

There is a knocking noise (like someone knocking on a door) coming from the engine compartment of my car. It's not detonation or pinging. The rate of the knocking sound seems dependant on road speed, not engine speed. It knocks about once every 2 seconds at 40km/h, once per second at 80km/h, twice per second at 160km/h. Slower road speed, the longer between knocking sounds. The rate of knocking seems too slow to have something to do with the wheels, transmission or engine... but road speed has a direct and linear effect on the rate of knocking. Also the noise is only apparent when on 1/4 or more throttle. There is no noise at very light or no throttle, regardless of road speed. This started when I came home from work last night, earlier that day everything ran perfect.

Does anybody have any clue whats causing this?

 

[Captain KRM P5]

could very well be rod knock thanks to a spun or worn bearing

 

[wannabe]

does it make this noise when sitting? have someone rev the engine, if you hear it then its engine related. if you dont, then its suspension/wheel related. could be something as simple as a centercap coming loose or a screw stuck in a wheel..

 

[deagz]

The noise isn't there when sitting. Only when in motion while on throttle. One knock sound once per-second at highway speeds doesn't seem like it could be a wheel... the wheel rotates many times per second at that road speed.