Hello all you wise people

Every 3 or 4 prints I'm having my extruder stop suddenly with a loud ratcheting noise, aka the filament blocked? It's that bad, that I cant even pull the filament out, after hotend is heated to 215c, without a pair of grips. Tonight it happened again (after a failed 10 hour print (twice)), extruder ratcheting, no filament coming out, print at 8 hour mark. Ripped filament out with grips, and decided to replace tubing, but that would not budge either, as it was welded inside hotend. Managed to rip that out with grips eventually, and cleaned the hotend out, which had black flakes dropping from it whilst doing so. Shoved a new nozzle on also, as that was not worth cleaning.

This is happening every so often now, and surely this can't be right? It's chugging away at the 5 hour mark now, so we will see if I'm successful for the third time on this print?, but it will only be a matter of time before the same happens again I suspect. Done all the usual, different temps, PID Tuning, speeds etc. Prints fine until late in the print?

Extruder is Creality all metal upgraded (the grey one), with a Noctua 40x10 fan cooling hotend, the part fan is stock. Capricorn tubing, which I'm suspicious about, as this seems to have started since using it?. BTT sensor (deactivated) just before Extruder (a worthless piece of nonsense which is getting removed when I can be bothered to do so, so a fancy filament guide ATM).

Marlin firmware, latest, and BLTouch fitted, and working great. 4.2.7 board, fans on PSU and mainboard upgraded to Noctuas also.

Any ideas guys?