Grinding sound from the front end

I have a 2000 Explorer Eddie Bauer with AWD and 64,000 miles. Recently, I have noticed a grinding sound (occasionally) coming from the front end when I brake. I had the brakes replaced yet the sound is still there. It can only be heard from inside the vehicle, more so on the front passenger side as the floor will vibrate. Here is the catcher, the sound will go away when I turn the Overdrive off. Put the OD back on, and there it is again, on occasion only. Any thoughts on what might be causing this?
thanks