Hello, I recently purchased 4210 combo. It is an amazing amp and sounds beautiful, besides one issue that I found in it. It makes weird crackling / buzzing noise on certain settings. That weird noise appears only on Boost channel on following settings: Gain between 9,5 and 10; Volume between 7 and 9,5. On Volume set to 10 there is no problem. Also Master Volume only slightly increases level of that buzz, so on high MV settings it is still there but less noticeable. Please find below two videos with the problem Has anyone ever faced such thing? What could cause a problem ? All tubes are new, replaced two days ago.