2 problems, servo pump and rear speaker

Again a hello in the round,

Our little one (2.8 Bj. 10/97, 200,000km) makes a few small problems.

The bigger problem seems to be the servo pump which makes very loud "quittle-whistle" sounds when the steering is hit strongly in the cold state. Servo oil is enough inside!! As soon as the engine is a bit warm, after about 500m, the noise is gone. Is the pump blowing? And if so, how do I get this sealed?

The small problem is the speakers at the back that only very quiet music comes out. When I put the fader fully behind there is hardly anything out there, is that normal or do the rear LS serve as a kind of "subwoofer"?

I just got a new problem. The battery has given up its spirit and thus also paralyzed the radio "Audi Concert". After installing the new battery, the radio wants the code. The code I have seems to be wrong and to belong to the original radio. The previous owner once converted to the Concert Radio. How do I get the radio again???

Thank you for your help!!

Greetings from Ingolstadt

Jörg