Hey guys,
Ok, firstly, thanks for all the helpful suggestions. I loosened the chain and that seems to have gotten rid of the horrible rumble, it still rumbles, but just not as much. The bike had a tensioner on one side, so you could effectively change the alignment of the wheel. But by being on one side, changing the tension of the chain like that messed with the alignment of the wheel, and hence the brakes.
Anyway, I took the wheel off and re-seated it a few times and it seems better. How loose should the chain be though? Now if I pedal (with my hand - bike upside down), their is quite a bit of movement.
Thanks again,
Daz.