I've done a lot of research to learn about the Aux Water Pump and am thinking this is my issue. The fact that I used to have solid flow of coolant through the system, constant flow through that little "piss" hole and back down into expansion tank --- which, now that I have this nasty sound AND there is no flow whatsoever...
My only question is, (and I'll sleuth it in more detail tomorrow when I'm underneath it), is that I see in this realoem link that there is a Water Valve located RIGHT where I am hearing the sound loudly; right near the air filter box:
https://www.realoem.com/bmw/enUS/sho...diagId=64_1115
Now, in all honestly, I did not get down on the ground, take off the engine splash guard, and listen down there - where the aux water pump is (right?). So, it may be loud as heck down there and only sounds like it's coming from the valve area. But, just an interesting development I wanted to share to see if it helps anyone diagnose my situation.
Thank you,
Jay