PM4 UPDATE: While still not my favorite headphones, I believe that I may have finally found a combination that cuts out the strange noise artifacts as well as some of the treble spike.
The Fiio E12, and KZ Starline Tips.
They have to be used together since just one or the other doesn't seem to fix everything. I'm using this combo both directly out of my LG v20 and also with the Schiit Fulla1. Both of these are colder/brighter sources, and the E12 does a good job warming the sound up without veiling the details. The E12 also seems to cut most of the treble spikes out on its own, but I still hear the noise artifacts from time to time.
The KZ Starline has a longer than normal stem and provides a decent seal with an opening that matches the nozzle width of the PM4 almost exactly. With the Starlines in, bass response is good, sound is a little less piercing, and the noise artifacts are almost completely unnoticeable. I think the extended length of the stem might have a lot to do with fixing that noise or resonance some of us have been hearing. It leads me to wonder if this is only any issue because they got rid of the long and short filters and replaced them with the mid length filter.
So, with the absolute perfect setup and right equipment, I'm willing to admit that the PM4s, as much as I've maligned them, have the ability not to suck. I don't know if that's enough to get me to spend a big pile of money on the Icarus IV, but it makes it slightly more probable.