Did you connect a Powerlink or RCA cable to one of the connectors? what do you see and hear when you do that?

No I tried without any audio cable because that to me should be a good starting point where I would expect red LED and total silence. If I apply a powerlink cable it is more or less the same with green LED and around same hum, but if I apply an RCA cable the hum gets a lot higher.

I have discovered that if the outer aluminium part is being touched it increases the hum. My assumption is that the aluminium part is/or should be "grounded" to the amplifier via the six screws? Another discovery is that when doing a short circuit of the RCA input the noise in the RCA switch selection lowers to nearly nothing. I have tried to see if the internal cabling is correct, and it seems like. It though wonders me why the audio cable runs directly under the transformer.

Okay, to finish up my own thread :-) my conclusion is now that there did not exist a proper connection between aluminium part and amplifier despite being screwed together. I noticed that the screws are some kind of black CED coated, and by working the screws back and forth several times the hum disappeared and the speaker now works as it should.

I noticed the same behaviour with BL6000. Basically, when you are in LINE IN mode,  you NEED to have everything terminated properly, even if there is no RCA plugged in. For my case, by BL6000 needs to be have Line-in RCA plugged in to the source using a cable, before everything is silent. If you don't want to plug anything in, you need to short the input via a terminating plug.

dear