I've got an annoyance with the car and can't seem to find out what it is nor can I find someone in person to figure out what could be the problem.

I've attached a picture of the "thing" thats causing a loud knocking sound with the hose pulsating as if it were a heart. I've used MSPaint to make two arrows showing what exactly is moving/knocking. It occurs once the car has been driven for a while and is fully warm. My guess its got something to do with ASD... but what and why? Any help/input is GREATLY appreciated.

The car in question is a 1991 190E 2.0 5-speed (Euro) tuned by AMG at Affalterbach. However, the part thats giving the problem has to be a standard mercedes part.