Can someone tell me what wrong


Hi there
i need some held with speaker hissing noise
i recently noticed some noise come from my right speaker 
the speaker is venture audio grand mk3 and driven by vta m125 tube mono block, it’s kind of loud, i can hear it from 4 feet away the speaker with the preamp turn off, it doesn’t effect by the preamp volume 
so here is what i did
Remove the preamp - still the same noise
swap the mono block - still the same noise
swap the speaker cable between left and right - still the same noise
hook up a vintage dynaco st70 - no more noise
hook up the right channel mono block to the left speaker - no noise 
so what could be wrong here?
I didn’t have that noise before 
This thing really drive me nut
Thank in advance 
 

128x128ownut
Way to go noromance! I’ve got an Ethernet switch in my system. Though I’ve not noticed any problems, how do I know? It’s always been there. Will a switch potentially cause cause the same problem as described above? 
@mbw Any electronic device can mess up the sound. In this case, it was a wi-fi transmitter which is as bad as it gets! Listen with your switch on and off. Any difference? That's your answer.
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@oldhvymec i think I will looking for a isolated transformer, but not sure yet