If you could be sure it's not a FAN motor or blower motor noise, but a sort of hollow-sounding/gurgling-type noise not long after unit is shut off (the noise gradually reduces in intensity), and assuming it couldn't be anything but refrigerant pressure changing-related, could you offer any possibilities then? If not, I'll just have to run it, and this time note (on paper) exactly what happens (in sequence) etc., record the noise and get back.Without hearing the noise, can't begin to make a reasonable guess.
As long as the unit is buttoned up, and I keep my distance should the compressor plug blow (its name escapes me at the moment), I'll assume I would probably be OK. No longer have the "partner" that was helping me when needed, but working on getting another experienced tech to look at this unit.
I should clarify that the noise I'm talking about now in this post relates only to my aforementioned experience (post #1) with this noise a couple of times (old MH pkg units), but wasn't loud like when it happened during running of the unit, before it shut down. Then it was a scary loud prompting me to immediately to shut it down, but if it's truly a pressure bleeding OFF/a combined hissing (internally)/gurgling-type noise, reducing in intensity as unit shuts down, I reckon it could be worse regarding safety while working on it.... or not, and I understand you have to be careful with your advice. However, the noise when it happened during running of the unit (scary loud then), is indeed the same type not loud noise described above when shutting down, just more intense when it was running.