Stuck calipers won't cause a grinding sounds..... unless they wear down the pads to metal on metal, but then the sound wont go away.

Probably have some dirt/rocks trapped in there. Take it apart, clean everything up, put some brake lube on the back of the pads and the arbor and you'll probably be good.

Check your CV axle (half shaft) boots and the axle itself for any play. Grinding could be coming from the joint if its worn.... it'll try to dislodge itself. Tapping the brakes may be reseating it.