2.5 TDI AEL Audi A6: Strange Noise?

Hello,

'Recently, I've noticed a new sound after turning off the engine. It sounds like a diaphragm pump or something similar, and it seems to be coming from the black box or the valve (?), with the three connections, near the mass airflow sensor (MAF). Does anyone know what this could be?'
And while we're at it, what exactly is the black box for - is it for creating a vacuum? Is it easily damaged?

I hope you can help me.

Best regards, Frank.