i have a 1997 audi a4 1.8t quattro. I recently installed a mbc(tuboxs) bleed type. I did it in the way where i bypassed the n75 totalls just left it electrically connected.I am chipped and i set the mbc to about 19 or 20 psi., the same the chip was set at just comes on sooner and smoother(no surge). Now my problem is when i come to an idle the car will sometimes tap. But the tap is heard right in front of the air box close to the firewall. It is a very odd tap because at first sounds like it is following the engine speed, but then picks up while the engine is still at idle and picks up almost to a fluttering tap and then slows down to a stop. Does anyone know what this weird problem could be? thought i bent something but realized it doesnt follow engine speed and then just stops on its own. The only thing i think i might not have did correct was i left the n75 where the lines use to go open. dont know if this could make a weird noise like that happen. and you dont hear the noise from under the hood coming from the engine you hear the noise in the cabin only with the windows shut but it is a very prominent noise. any help would be greatly appreciated. thank you

 

There is a pcv componet that does make some ticking/tapping noise mounted to the air box there, take off the plastic cover and see if you can pinpoint the noise better