I have a similiar problem
My rear drivers wheel is making a similiar grinding noise. Mine is not speed related. It makes a couple of crunching noises rolling to a stop the last two or three feet and makes a final crack just milli seconds after the vehicle comes to a stop. The garage I took it to says it sounds like the axle. I don't want to replace the axle and then find out that wasn't the problem. Now a piece of the parking brake assembly on the passenger side fell off at the garage parking lot the day I took it to get checked out, but again this is from the driver side. I didn't think about a brake issue until I read this thread. A wheel bearing would be cheaper than an axle. I just don't want to waste money to find we repaired the wrong thing. Please let me know, thanks. Oh it is not the brake pads, they are still thick and I can see them and nothing eating away at the discs or pads.