Tube amp buzz while turning up volume

Hello fabulous people in the space! Really appreciate any input on this issue I'm experiencing with my tube amps.

So I just bought an EVH 5150III 50S 6L6 amp. I noticed buzzing when I turned up volume on any channel. I can't figure out if it is power tube or output transformer but the sound comes from that area. I link a video I shot with iPhone showing this issue.

At first, I suspected this amp had problem out of box. Then I tried my other tube amps also connected to BOSS Tube Amp Expander attenuator and 212 cab. With TAE speaker out volume all the way down, I could hear the same buzzing noise from my other amps too! Which I don't recall hearing before...

So I suspected it might be the BOSS TAE. I then tried with UA OX, with and without amp selector in the signal chain. Same buzzing when amp volume turns up. Tried different instrument and speaker cables, same thing. I didn't bother trying with Two Notes Captor X. (Direct connect to cab is not an option right now due to volume...)

Well, usually I would suspect power tube issue, but it just can't happen that all four amps having power tube failure at the same time! Or can it? Granted I hadn't powered on the other amps for more than half a year due to family priorities. Now I have no clue which area to trouble shoot next:facepalm:









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