Cause : Fuel filter
I changed my fuel filter a few days ago and I haven't heard it pink since then! There seems to be a rattle from the cat heat shield, but nothing like it was before. I gave it quite a good test, too it up a steep hill, let it struggle for a bit, and it was silent :-o. There have been a few similar sounds, but they hardly every occour and I think it's just the normal sound of the cat heat shield.
Can anybody explain why/how it made the pinking kinda noise? I think the noise was being made by the cat heat shield, but the fuel filter was causing this some how. If there wasn't enough fuel I would've expected the car to just be slower. The heat shield rattle is fairly constant, smooth and quiet now.