[DreaF]

Wenn es sich so anhört, ist es die Vakuumpumpe:

https://www.youtube.com/watch?v=DT_K8VRFtp0



http://www.promini.com/technical/tech_ti...-noise.php

Du findest dort auch das hier:

unter 3. :
If the noise appears to be coming from the valve cover or the vacuum pump area, refer to SIM11 02 08. To verify the source of the noise, disconnect the vacuum hose from the mechanical vacuum pump to eliminate the knocking noise. This is not a failure of the mechanical vacuum pump; do not replace any parts.