As Miro666 has already mentioned, the awful stock soldering job on the tweeter terminals at the motherboard are the culprit.
Since there's nothing much more I can add to his answer, I'll just describe my process and post a couple of pictures of the problematic solder job, so anyone else facing this issue can easily locate it:
- Same as Miro666's solution, remove the screws and take the back off (gently, as the speakers are connected with thin wires)
- What I did here instead of Miro666's suggestion, is take out the 4 screws connecting the motherboard with the heat-sink as I found it a lot simpler than disconnecting the very inaccessible spade connector from the tweeter.
- Same as Miro66 solution, locate the underside of where the tweeter wires connect to the motherboard (pic included)
- In my speaker, it was the more common case of an unnecessarily huge glob of solder, bridging both traces causing the issue.
- Opted for completely re-soldering the points instead of scraping away at it, because as you can see by the sheer amount of solder that would've been a nightmare. A clean tip, some fresh solder and a cheap solder pump and job done - the solders now look like this:
- That's it! This is a good time to refresh the thermal paste on the heatsink connection spots if you wish, otherwise re-screw the motherboard onto the heatsink and re-screw the entire back panel into the speaker box.
I don't think they soldered this particular spot on the production line. Seems like a hacky, quick fix for a missed solder spot, because the other tips are soldered with factory perfection. Not sure what happened here, but hopefully this fix keeps.
Thanks to Miro666 and all the people that contributed, hopefully Presonus have acknowledged this super annoying issue, and improved their supplemental solder jobs, especially since a lot of people really like the monitors themselves.
Cheers, hope this helps someone.