cl500 probs

After a 2 hour high way trip i noticed when i came to a stop i could hear a weird knocking noise coming from under the hood. When i accelerate it doesnt seem to be getting louder, its a constant noise, which seems to be coming from the front left of the car/engine. . It's hard to describe their for i made a video. My car is actually a w215 2003 cl 500 but since it has same engine as the w220 i decided it be more helpful to post it here.

http://www.youtube.com/watch?v=1xbT8...ature=youtu.be