Thanks a lot Florian!
Mind and Body: after a few minutes of settling down, the object pops into clear focus. Noticeable shift.
I think that I have noticed this one before - there was a change in where I was perceiving thoughts, instead of them being at their usual location, it was as if they have moved forward, becoming easier to observe as something other (ie. not my thoughts, just other sensations). I have not noticed this shift in a while.
I am not certain whether I notice a difference in clarity - there is a difference in how sensations appear (sharper/duller) and my attention changes too, I will have a look at this some more. There is also a change in propensity to become immersed in something (visual/thought/pain/misery/analyzing/planning), which changes from time to time (ie. there is something else that I am more likely to immerse in rather than observe it). If I stopped enjoying/hating certain parts of the process, it would all be a lot easier :-)
Predominant sensations: To me, the meditation object presents in subtly different ways over the course of this development: the breath can be very mechanical in some stages, present in short or longer pulses, and so on. The "inner sound" will be focussed or diffuse, chorus-like, bell-like, etc.
This is not entirely what I meant - for example, I get a humming noise in my ears a lot but it only seems to fit into a certain part of my meditation (I suspect A&P but I am not at all certain that my attempts at identifying stages are anywhere close to home at the moment), equally visual activity changes a lot (it can be flickering, sometimes it is very vivid, sometimes there are black blotches here and there quickly coming and going).
The build up/crash thing, provided we're talking about the same thing here, is likely "energy release" or subtle tension or attention breaking into places that were obscure so far, or however you like to frame it.
That would make a lot of sense, the first time I noticed the shift was when I went running and there was a perceivable change (a build up of sorts) between being in pain and being caught in feeling miserable to catching second breath (disembedding from the pain and a shift from misery to acceptance) - it wasnt just that one changed into the other, there was a shift in between. I have sometimes (rarely) noticed something similar during a sit.