SonyActiveSubwoofer quiet pulsating sound and continuous when connecting chinch

[DerTechniker]

Hello,

the Sony SA-WMFP85 Aktive subwoofer makes a quiet pulsating sound when nothings connected, and a continuous loud sound when chinch cable is connected.
Power light and starting is as usual, fuse is ok, all parts seemed to be ok (not burned).
Do you have any idea what malfunction it could be or what should meassure? (Service Manual in attachment)

greetings

 

[Bruce@bluff]

Sounds like a grounding problem, check for dry joints also that the outer ground part of the rca ( chinch ) socket is connected to the 0v point of your psu