Joar wrote:

- Every time I start the Beocenter and touch "sound" the bass is put to minimum. Is that a factory setting? I checked the user manual but without success.

It's not a factory setting.  You should be able to set the sound settings to your preference and then press PROGRAMMING SOUND STORE to store them, so that these settings will be retained when you turn the machine off/on.  If it is not keeping these settings, I would suspect a faulty battery inside the BC9500 - this situation would be compounded by turning the machine off at the mains when not in use.

Joar wrote:

- There is a humming (electrical) noise comming from the area where the inputs are, above the tape deck.

Mine buzzes, but from the transformer on the far right of the unit, behind the CD - perhaps yours originates there?  Such buzzing is fairly typical of older transformers as the metal plates loosen up over time.  I just accept it!  You could check that the voltage selector on the reverse is set to your local mains voltage.

Joar wrote:

However when switching on the speakers will make a short cracking noise

This is normal, and another good reason not to switch it off at the mains!

I'll try to find some threads about battery changing.

(Edit - just added 'Programming' before 'Sound' and 'Store')