EARLY timing belt failure. Here's the sound I heard for 25 miles before it happend.

This mysterious broken camshaft sprocket happend to my 1994 Mazda MPV JE 3.0L V6 SOHC 18 valve engine. Watch the full video on my channel for further details.
Over the course of two weeks and approx 20-25 miles I heard an unusually loud rattling sound throughout the entire valve cover on this one cylinder head.
However even using a mechanic stethescope I didn't hear any unusual sound coming from the timing belt cover and camshaft sprocket area.
Then one day while driving approx 40-45mph, I suddenly lost power and heard a horrendous engine sound.
*What could have caused this??*
Engine oil maintenance has been followed meticulously and timing belt with all components including camshaft/crankshaft seals were replaced 30, 000 miles ago.