sounds like it could be a rock. Try backing up, turning the wheel and applying brakes to see if it dislodges. Shouldn't be anything major - worst case you'll need to pull the wheel to get a better look.
Thats what I'm thinking... It's hard to replicate it also... I just went for a 20min drive and it was silent. Maybe the little rock got out of there.
I'll try what you said though!
Thanks!