Hello Gothaur,
thanks for you question. You're right, the steering pump sits behind the seats. There is a word missing. I've meant steering pump system. Sorry, English isn't also my first language – i'm from Germany.
The hydraulic steering gear box is located in the lower front. There are some valves in there that can do noises. See attached photo.
On the right front side there is also the brake booster. If you open the frunk you should hear if it's coming from there. Intermittent interval could maybe be caused by the ABS system checking pressure. But in general this should lead to a warn signal.
Did you put the car on a diagnosis system and check it for error codes?
Regards, Markus