Sounds like a bearing problem,
Jack the back end up and spin the wheel if the bearing is worn you will feel a vibration through the spring, you can compare each side.
Also dont be tempted into greaseing them as that will do nothing if the bearing is worn the damage is done,
Also if your better of getting somone who knows what there doing to help or do it for you, as the bearing is what holds your wheel on, you dont what to get it wrong as if it fails at high speed you will be in a lot of trouble