New Discs - still got a vibe

Any idea what would still cause vibration when applying brakes - new discs and pads fitted, everything balanced on front. Only get it (through the wheel and pedal a bit) when braking from higher speeds, don't notice at slow speeds - manifests itself as a 'grabby' feeling at low speed. Ideas?
(Think I have CV joints on way out -specially on offside - can they be related?)