Very easy to change man. They're called cush drives. If you pull your rear wheel off, your sprocket hub just sits in the wheel and thats where the cush drives are. How old are your chain and sprockets?If I understand correctly, there are rubber shock absorbers in the rear hub to cushion shock on the driveline.
Is a small vibe in the rear when taking off (gently, even) that they may be worn?
How expensive/how hard to change?