Can the rear balance valve cause pulsing if faulty?

[Mags]

I'm getting a weird brake pulsing just like a warped disc but only when I brake hard and generally downhill. It doesn't seem to be there all the time and although I will check my discs at the weekend I'm not convinced its a warped disc.
When I got in my bus yesterday it did it right away regardless of how hard I braked, as my journey went on it stopped doing it and then I only noticed it at the end of my journey again if braking very hard, It sounds more like a knocking noise from the front end than a warped disc so I'm thinking it might be something else, I'm confused.
My front end is a Red9 wishbone setup, I've checked every bolt is tight, no play in the wheel bearings and almost everything is brand new although the discs are not, so I will check this out with a dial gauge first, any other suggestions welcome.

Mags

 

[gvee]

Just to clarify: servo assisted brakes? If so check that the vacuum line is good (it might be collapsing on itself somewhere) and the one-way valve is working correctly.

 

[Mags]

No servo