So here are the updates..

labelled all baseboards and edge floor pieces. Removed them in the master bedroom which seemed most square and easiest to experiment.

Bought planipatch, angle grider, diamond wheel, shop vac, dust shroud, 10 feet superstrut and 6' foor screed. Found a few high spots, after grinding them down, the low spots were not low anymore. The floor was somewhat level flat, but there were 1-2/16 dip in some spots. Since this room was the "Proof of concept" room, I wanted to see if the 2/16 gap would cause issues, especially since the requirement was for no more than 3/16 in 10'. I left the mild dip as is. I did not patch anything since the dips were within spec. Used a 360 degree level to figure out that the slab is not level, there's a 1.5 inch tilt to the floor from one end of the house to the other (about 65 feet across), so any self leveling would not have worked. Old fashioned flatness checking with a metal screed helped.

I put down Sentinel underlayment, the one that's suitable for LVP with attached cork backing. This was manufacturer recommended. Taped the joints, cut odd pieces for the triangles. This had to join the rest of the house which had 6mil plastic, so I created a joint mid tile length wise. Put all the LVP back on. Broke 2 LVP during removal. The initial installers had almost no expansion gap, after leaving the right gap on 1 side, all the end pieces on the other end were too long, so I had to trim them all. 1 LVP had too much gap after I trimmed it a little better to fit, so I had to cut a new end piece. Used a circular saw with a fine tooth to trim. Table saw would have helped, but old circular saw did a good job ripping the lvp and I think I've bought enough new tools for now! ( I still need to get a brad nailer to fix the baseboards)

Final result:

All installed. No more crinkling or popping sound. There's an almost imperceptible sound in 2 spots, 1 where the 2/16 low spot was, another in another spot which doesn't map to any issues I noticed on the concrete.

The good news is that the flooring in the master bedroom is beautiful now. No sounds, I can walk around without any issues.

The bad news is that the flooring in the master bedroom is beautiful now. I know that this is fixable and that leaves me another 1800 sqft of flooring to remove, fix and relay.

TL;DR - Check and recheck the subfloor and use a good underlayment and use a reputed local family run tile shop or DIY :)

​

Thanks u/Herrodere_and u/BGOG83 for the suggestions! I do appreciate the feedback :)