noise from under the hood after drive
 

My car is 2009 3.5d, maybe 3 or 4 out of 10 times, after driving and shut down the engine, I can hear some noise under the hood, at the front of passenger side.

There is a square box, with a bunch of tubes on it, behind the DEF filler. Does anyone know what that box is used for? I feel the noise from that box or that area. Not sure if this noise represent something is about to fail or it's normal. The noise goes away after 1 or 2 mins.

Here is the video I took just after driving, You can hear oil is dropping back to the pan. The noise goes away close to the end of video.

https://www.youtube.com/watch?v=Wg3S-pB-5CM

Turbos cooling. Normal.

That is the active tank and the transfer pump is filling it up from the passive tank.Normal vehicle function,nothing to worry about.

Thanks guys, I believe bawareca's answer is correct. I know my car's passive tank is empty because I got 1000miles no start before and I refilled active tank only.

After I filled 2L in the active tank again, there is no more pump noise coming out any more for now.