Strange noise after stopping engine, A160

[Lingu]

I dont know much about cars, but could someone help me out about that problem with MB A160.

When I stopped engine, some strange noise still came from under the hood. It came from some kind of pump (or something) that is located on the right side under the hood, quite close to the window cleaning water tank (kind of left and below it). Also some kind of a tube is going from that pump to engine.

I thought at first that it is used for engine cooling and could be supposed to stay on for a while, after stopping engine, but the sound got worse and worse and the same thing has never happened before, so I pulled off an electric wire from it, that made it stop. When I reconnected the wire later on, the pump started to work again, even though I had not started the engine.

I would be grateful, if someone could tell me what is that pump (or whatever it is) for and what could be the problem with it?

P.S. I am sorry about my terminology, I really dont know much about cars yet.