Fiesta Mk6 1.4 16v 2004 - Help with diagnosis - splat90

So got a tap / rattle that appears to be coming from the cam belt side of the engine. Most audible at 2000rpm. Also engine drives fine.

I'll link a couple of videos of the noise being made.

Cold Engine - youtu.be/ckRge9GVfIE

Warm Engine - youtu.be/KtdYYZ9bp-8

The engine management is due to O2 Sensor, which I replaced this time last year and failed again.

Any help, advice or diagnosis welcome at this point.

Edited by splat90 on 13/04/2017 at 18:36