This guy is just wrong that the amp is shipping with a defect that causes a whistle. Moreover, just because his MKIII does not have the issue in no way proves, supports, or provide any evidence that the RI has an issue. The MK III is not the same amp. What if he has a lower gain tube in V1, which is why it does not go microphonic.
Simplest answer to the problem is a microphonic tube. If you have been around tube amps long enough, you just recognize the sound. Maybe somebody should tell him about tapping on the tube with a pencil to see if it goes microphonic. He should set the dial just below the point at which it sets off the self-oscillation and then tap it. It should start to oscillate.
When my MK VII arrived, I started to set the dials for my high gain sound. As soon as the treble hit the higher end of the dial, the amp went into self-oscillation. I found the tubes causing the problem, replaced them with some high gain tubes, and the problem went away and I have not had it since. My MK III, same thing. I spent a good many hours finding the right combination of preamp tubes that were high gain and not prone to going microphonic.
I should also note that that kind of whistle can be caused by a lot of things in a complex guitar rig. I use Mesa Head Trackers in both my rigs. When I first installed them, I got all kinds of whistling. The culprit was bad cables causing a grounding issue. Ground loops can also whistle instead of the usual buzz.
I think it is crazy to encounter a problem like this and jump right to the amp has shipped with a defect. I think this is some kind of Gibsonitis that leads people to jump to these conclusions. Tubes do get damaged in shipping, not matter how well the amp is packaged. How many gentle FedEx and UPS delivery people do you know? Modern production tubes are not up to the realities of shipping these days. We need some modern production JAN type tubes.