The hum (50 Hz) comes from the 220 volt supply network and is caused by current power flows through the protective conductor. These so-called "ground hums" is caused when you connect two devices that are already grounded on the protective conductor (subwoofer) or the antennae cable (AV Receiver) to the subwoofer cable.
Solution:
Separate the direct connection by a grounding filter for the antennae cable that is created for it - for instance, the Teufel modell sheath current filter AC 9022 ED. Alternatively, you can use a galvanic separation filter that is looped into the connection between the subwoofer and AV Receiver.
The hum disappears if the antennae cable is separated from the Receiver/Tuner/TV. First try the grounding filter, otherwise the galvanic separation filter.
Solution:
Separate the direct connection by a grounding filter for the antennae cable that is created for it - for instance, the Teufel modell sheath current filter AC 9022 ED. Alternatively, you can use a galvanic separation filter that is looped into the connection between the subwoofer and AV Receiver.
The hum disappears if the antennae cable is separated from the Receiver/Tuner/TV. First try the grounding filter, otherwise the galvanic separation filter.