It's my understanding that the brain's processing of sensory information is discrete in the sense that if two sensory impulses arrive close enough to each other (about 20 msec), they're perceived as simultaenous. Yet our experience appears to us as continuous. My guess would be that meditation involves opening conscious access to earlier processing stages in the brain, where our sensory experience still seems somewhat discrete - thus the "vibrations".

This would seem compatible with e.g. this paper, which hypothesizes that meditation reduces the amount of end-stage processing in the prefrontal cortex, as well as various reports from meditation practicioners which also seem to involve access to earlier processing stages of sensory data (e.g. being able to separately perceive a raw sensory input and the resulting emotional reaction to it). It would also explain why learning to see the vibrations would lead to an ability to see the concept of self - or the "label of the observer", as the grandparent calls it - as something arbitrary, if the same process also allowed us to see part of the normally pre-conscious processing stages that constructed the sensation of a coherent, unchanging self.

Though it should be noted that this process of deconstruction seems potentially hazardous for one's mental health: once you start seeing just how arbitrary your self and world-image is, it can be quite frightening and disorienting. Suddenly some of the concepts which your brain has used to order and understand reality with just stop working:

And this can be an attenuation in self or it can be a complete dropping away. And even though you can read about this and think that this might be the goal of the contemplative path. For a lot of people it’s very very scary when that happens. And so when I mean dropping the sense of self, it can be a lack of a feeling like there’s anybody controlling. So one word are coming out of the mouth like who would be speaking them. When you move your arms and legs and walk it’s not really sure who decided that. When somebody ask you a question there’s almost a panic feeling because you don’t know who’s going to answer the question. There’s a sort of temporal disintegration. So the sense of time can fall apart, along with that your sense of a narrative self over time. Part of the sense of self is about being able to have continuity over time. And if you just don’t have that kind of sense of past and future and you only have a sense of now, your sense of self just by not having a past and a future and being able to imagine that can be sort of truncated and attenuated.

And then temporal disintegration can kind of go even further beyond that where people almost like they’re waking up in a new reality every several minutes. And they don’t really have any way of describing the reality that came before that and it can be very disorienting. You can wake up and really have to study your environment to figure out who you’re talking to and what the conversation is about. You can learn to get good at that, but it’s pretty disorienting for a while. And then I don’t know if this go in order but I think that the most common symptom, it’s hard to say but again these are all really common, but one of the most common symptoms is fear. And the lost of the sense of self I think is very tied in with this fear. And people can have really phenomenal levels of fear. I mean really just existential primal fear.

Likewise, if the process involves greater access to unprocessed raw data (including raw emotions) and a reduction in the activity of the prefrontal cortex which usually regulates and mediates those emotions, that's going to cause a lot of trouble as well. I suspect that these are the causes of the so-called "Dark Night", a stage in meditation which may cause serious depression and clinical impairment until it's overcome (via more meditation). That's the reason why I actively avoid trying to see any vibrations for now - maybe I will eventually go there and risk the Dark Night, but for now tranquility meditation seems to avoid that while still having major benefits.