different kind of clicking noise

When my car is moving my back left wheel makes a clicking noise. Any idea of what it could be or if it's bad?

do you have drums on the back? if so, a piece might have broken or became loose and keeps falling inside like change in a dryer. . . or it could be the self adjuster for the brakes not locking in place clicking on the adjuster bar. . . or you could have a quarter roll of electric tape that was on your garage floor when you wired up your buddies stereo system that got stuck on the wheel hitting the wheel well.