As time's gone on, I've realised that the rattling from my engine is not down to the tappets, but from the pulley shown below that is clearly a bit worse for wear:
I can see it vibrating as the engines running. (You can see the bolt on the tip of it is a bit fuzzy in the picture as its vibrating) I can't get any movement out of it when its off though.
What pulley is that? Is it just an idler? Will have to get that sorted ASAP as I doubt it's a good thing!