Sounds like a hot signal. the rocker's + highs setting increases gain of high frequencies, which increases distortion of high frequencies if it's a hot signal...
Easier to hear on lower notes though, because they tend to drive the amp harder in terms of voltage/gain, than a higher note, but they have harmonics that are in the high frequency range boosted by the + as well...
Try changing the sensitivity switch's setting. I should say, the lower gain setting is what is 'stock' on the V4b which doesn't have any sensitivity selection. That switch actually changes the headroom of an early preamp tube stage (kinda). You can fiddle with the volume knob from there and see if you get the same issue.
It may not be that, but it's worth eliminating, even if that isn't the issue.
Also, some level--sometimes a high level--of vibrational noise/microphonics is normal. Most amps have a lot of signal gain going on. Tubes also kind of amplify 'mechanical/vibrational' noise. Try turning up your amp sometime and tapping on your power tubes with a chopstick (start lightly). You will be surprised. Likewise with each tube. Thought some tubes and some tube positions do it more than others...
If you can record the buzzing, it would help. Like a real speaker recording--you'll nail down and see if it's speaker audible or a buzzing you are hearing in the room. It's hard to differentiate at times, oddly. However, if you capture it through the speakers, we'll know more. It could be so many things - a speaker issue, something loose, a misbias...so many possibilities. Audio might help if the sensitivity trick isn't doing it.
Easier to hear on lower notes though, because they tend to drive the amp harder in terms of voltage/gain, than a higher note, but they have harmonics that are in the high frequency range boosted by the + as well...
Try changing the sensitivity switch's setting. I should say, the lower gain setting is what is 'stock' on the V4b which doesn't have any sensitivity selection. That switch actually changes the headroom of an early preamp tube stage (kinda). You can fiddle with the volume knob from there and see if you get the same issue.
It may not be that, but it's worth eliminating, even if that isn't the issue.
Also, some level--sometimes a high level--of vibrational noise/microphonics is normal. Most amps have a lot of signal gain going on. Tubes also kind of amplify 'mechanical/vibrational' noise. Try turning up your amp sometime and tapping on your power tubes with a chopstick (start lightly). You will be surprised. Likewise with each tube. Thought some tubes and some tube positions do it more than others...
If you can record the buzzing, it would help. Like a real speaker recording--you'll nail down and see if it's speaker audible or a buzzing you are hearing in the room. It's hard to differentiate at times, oddly. However, if you capture it through the speakers, we'll know more. It could be so many things - a speaker issue, something loose, a misbias...so many possibilities. Audio might help if the sensitivity trick isn't doing it.