Full System Freeze and "Crash" with loud Audio Pop (PProCC 17/18)

I'm having issues with my iMac 2015 (Specs below). Pretty much using any project and any flavor of settings I'm getting full system freezes (crashes). And it happens in a variety of ways. Tonight it was the Text Tool... sometimes its dragging footage on the timeline or during playback. But the crash is always the same. A loud audio pop, system frozen and then I swear into the night.

I've been trying for a few months to find a remedy (been an a regular premiere pro user for nearly a decade), yet it almost always ends in naught. Sometimes I can get large streaks where everything works. But inevitably it just hits the crash train and will freeze for days on end. The best guess is it has something to do with GPU. When I turn that off and use Software Only I usually have extended success... but whats the point of using items like Lumetri (and other GPU accelerated effects) without getting the GPU involved. And BTW when it works, the GPU and Lumetri effects are fantastic. But nonetheless the problem persists on a consistent basis.

I've tried brand new projects, week old projects, maximum assets, minimal assets, proxies, no proxies... 2k, 4k... ProRes. External drives, internal drives. I've tried PPro 2017 and PPro 2018 on Sierra, and High Sierra... the nuclear option, full brand new installs of OSX. Even had Apple do a wipe themselves. We've run diagnostics and nothing comes up as having issues in the hardware. There seems to be little or no consistency for crashing/freezing.

More frustrating, I hook the same exact same project (and I've tried about 20 of all sizes and shapes) to my Retina MacBook (2012 mind you) and its flawless. So in a jam I'm covered. But again, sort of minimizes the point of using a 27 inch Retina iMac and 32GB of ram as a proper "desktop".

The worst part is when the iMac freezes. Premiere doesn't crash (leads me to believe its hardware / despite what the system says), so I have no log to even have half an idea what freaked out (some kernel panic) and sent the machine into a tailspin.

The rest of the creative cloud has been flawless... I regularly use 7 or 8 other applications and rarely have issues with them. Which then leads me back to thinking its Premiere.

So thats my story... I'm at my wits end and I'm looking for clues and suggestions. Any places I might not be looking?