Hey mate, I know exactly what the problem is. As you said your pump is on its way out. Have you got the ST wheels on?

I had a set of 17, 205's On my Fiesta, And the power steering pump started out just like that making noises, Then it just went as I was driving along, which wasnt good

Either put smaller wheels on, Or start shopping for a new pump. My car is still under warrenty so Ford did mine for free! But good luck gettin it sorted