Thanks for all the replys guys. I've taken the disc off & put it back on carefully 4 times now and it still hasn't resolved it. I was looking at the disc closely and it does seem to be warped slightly as there's a ring worn into the disc from the pads and on one section the ring hasn't worn in
Suppose that's what i get for buying a cheap replacement off the bay. Not only that when I went to put it back on the last time, one of the bolts has snapped off when I was torqueing it up
Proper cheap bolts they use on these bikes. Even though it had an 8.8 stamp on the top of the bolt, seems unlikely it's actually a 8.8 bolt if it snapped before torqueing up to 10nm (which seemed awfuly low for m6 bolt?)