Ford Focus 2.0l Petrol - 2000 - ABS Brake Problem?

When you reach 33mph there is loud noise that appears to be coming from the braking system.
If you then apply the brakes under normal driving conditions, you get the same feeling as if you have braked on gravel - ABS normal operation.
If you accelerate to 33mph again the noise starts if you slow down without touching the brake pedal at 15mph the sound changes, when you get to 0mph vehicle wheels just moving the noise stops.
Less than 33mph there is no problem with brakes and they operate perfectly
About 6 months ago all the brake pads renewed and all brake discs, no problem until now.
I would appreciate your views.