Also, regarding the high/low notes in the UA sounds, have we ever confirmed/disproven whether there's a repeating pattern in those? A non-repeating pattern would pretty well put to rest the idea that there's a message in there.
Not conclusive either way IMO. In my own research and looking back at the previous threads, there is no recognizable pattern... but that doesn't necessarily mean there isn't one.
From my own research, some of which is confirmed by old threads, after-the-fact:
-Purrs are either hi or low. easier to recognize when sped up, but not required.
-Purrs are exactly the same "notes" before scooping. After scooping, purrs gradually increase in pitch until UA dies (but still form hi/low sequences). possibly related to UA decay.
-Before scooping, there are 2-3 purrs per set. Afterwards, there are 6-8 purrs per set. Sometimes the last purr is somewhat obscured by the howl. Also the first purr can sometimes be quieter than the rest.
-The howls always alternate between 2 distinct types, e.g., it's always [purrs > howl A > purrs > howl B > purrs > howl A > purrs > howl B] etc and it doesn't matter if it's been scooped or not.
-First UA I recorded had one sequence of hi/low notes. 2nd UA (in a different system) had a different sequence. Not sure if this is significant or not. I personally haven't tried retrieving a UA and taking it anywhere else and recording it for the purrs, although I think others have done so.
-There may be a "begin transmission" purr close or on top of the first howl. There seems to be an "end of transmission" purr immediately before the UA dies. UA#1 end-note was opposite that of UA#2 end-note.
The testing I did to determine the above, was completed at the location the UA's were found in the "shell". Didn't transport them anywhere.