Yes, most people get this from minoxidil (me too). Starts after about 2 weeks, but you can handle the problem with KET-shampoo (or head and shoulders anti-dandruff shampoo).
I get it and its just the minoxidil flakes drying up and flaking off, its a pain in the ***..
I combed about 200 flakes from my head (seriously) it was f*****g horrible...Now I make sure i wash my scalp properly rubbing the flakes off in the morning. So the build up doesnt get too much.