Passive loudspeakers usually only reproduce the hum, the cause is usually the amplifier or the connected playback devices such as CD players or turntables.

By testing the playback devices, the cause can often be narrowed down. To do this, disconnect the cables of all playback devices that are not currently being tested.
If a playback device triggers a noise, an improvement can be achieved by turning the mains plug in the socket. If this does not change anything, the signal cable should be replaced.

In the case of humming noises, filters such as a "sheath current filter" can eliminate the interference.
Mobile phones, radios and powerful household appliances in the vicinity of the system can also be the cause of the interference and should be switched off for the test.

If these tips do not eliminate the noise, the devices should be checked by a workshop.