Not that i want to spread salt, but...
How would a big end failure show up in compression test?
A Swedish guy had exactly the same experince, fairly quite at idle, and increasing sound as revs went up. When he opened up the engine, he found out that the flywheel side main bearing was shot, and had rotated in the block.
I heard IRL an engine that "died" on a track day. It came "suddenly"... That was a big-end, and again, it was fairly quite at idle, started knocking from 3000 rpms.
Weird though that there was no metal in the oil, so maybe you're lucky. I'll keep my fingers crossed that it is something cheap

Defining/describing noise over the internet is not easy. Knocking is different from ticking/pinging, but how do you describe knocking, and how do i interprete it?