Cyclic thumping sound from rear wheel

[asshanson]

This is on my girlfriend's 2001 Escort zx2, when going around right corners somewhat fast the rear end seems to have this clunk/thump sound which sounds to be directly related to how fast the wheels are spinning. Not on left corners though, so I'm thinking it's the rear driver's side wheel area since that would be the outer wheel getting more force on a right turn. It doesn't make any sounds under slow turns, but gets louder the harder you turn.

Any ideas what it could be? It's got 95k miles on it, all original parts.