FIXED!
New pads fitted, and the knocking has stopped. As I was stripping down the callipers to remove the Mintex pads, you could actually feel movement in the outside pads. Once they were off, it was VERY obvious they were moving about inside the calliper.
Calliper off, gave it a good scrape as well to remove a build up of brake dust
Old pads off. You can see where the black has been removed around the outline of the calliper
Side by side with Old and New
Old pads after a wipe down. You can really see where they have been moving around! They have only been in 5 months
