New on this forum

I have a 1992 Audi 100 2.3E Automatic and it's got a knocking sound from under the shifter when idling. If I push the brake pedal in the sound stops. If i pump on the brake pedal I can hear the knocking in the same frequency I pump the pedal. I think it's strange the sound is right back where the shifter is and not in the engine bay. It can't be the vacuum pump then?

(Sorry for the english...)