Just read this with interest......coz ive got a similar prob.....tho not as bad....
Admins feel free to start this as another thread....but i thought another brake problem thread was one too many

When my front brakes are hot slight squeal when brakes lightly applied....develops into a grind when pressed hard.....slow moving tho....less than 20mph.
They've been slightly sqealing for a couple of months now.....last couple of weeks grind noise has started.
ie as you get to about 20mph slight squeel starts and then at the last moment before you stop i can hear a slight grind noise
New vx pads and disk about 10k ago.
Took the pads of today (plenty of wear left on em) and sprayed generous amounts of brake cleaner on the disks and pads....put em back together and its made bog all difference

Gave the outside of the pads a good dose of copper grease first too
Should i try new pads next.....or is it worth getting a power sander on the pads to ruff the surface up a bit....to see if this does the trick?? :-/