vacuum pump vacuum noise

[tadco]

My 1980 300D is making a buzzing (vibrating noise). It started when I changed the vacuum lines that run from a vacuum T which branches from the main line and feeds the modulator valve and the white plactic item on the top rear of the injector pump. The noise started then. All I think I did was shorten the lines. What does the plastic part do and why is it making noise?

The lines to the modulator valve have been bypassing the valve device mounted on top of the valve cover for some time. When I inserted a vacuum conector tube in place of that vavle, which is activated by the accelator pedal, a late shift problem stopped.