Greetings,
Pavel:
This lasted only a short moment and repeated once more a couple of days later, never since.
This could be an A&P event, which is mentioned in MCTB... but since you say you have not found anything of the such described, perhaps you would find this to be of interest: (http://actualfreedom.com.au/library/topics/pce.htm). I am guessing that most people would not know the difference in experiencing the two, and would very much confuse the two depending on the context of one's path, one's intent with one's practice, and one's background in these matters, and so forth. To the point, I had a PCE during 2nd path and wrote it off as something Siddhi related or perhaps a "weird A&P," only to find out later that it was a completely different and distinct state. The finding-out of such was done a good month or so after attaining arhatship, which is significant for a few reasons I won't go into.
Pavel:
The thing that was strange was that it somehow seemed as if at first there was the awareness of something, followed by something/someone being there to experience it. In other words, there was an immediacy of experience followed by someone quite rudely crashing the party and being actively aware of what was being observed, the flavour of the experience changing in that there was an addition to the experience itself.
Ponder this and see if it is reasonable: the first awareness was the body's sensuous awareness; it is the body's actual physical awareness of the actual wave of sound entering the physical ear drum. The second is one's self identifying and/or representing the sound to itself, as if to "echo" the actual sound to itself to check to see if any reaction is necessary based on one's identity (such that if it was a sound of screaming, the echo may cause fear to well up). Note that enlightenment will not remove this identity as to be a bare awareness (what is witnessed in a PCE), but instead it will shift it from being a personal identity to an impersonal identity (the nature of this process is universal, whereas the content of what is identified with would be idiosyncratic). The impersonal identity typically makes much less a fuss about what it finds, and so may be less "rude" and perhaps more predisposed to "partying nicely," but I would recommend getting rid of the whole mess altogether.
Perhaps that helps you, but I won't say more as it is really up to you to digest and then decide what to do with the information provided.
Regards,
Trent