How to get rid of the annoying 'clunking' noise from my Altea's rear axle?

I've had my 2004 Seat Altea for a few years now and recently noticed a clunking noise coming from the rear axle when I'm driving over bumps or making sharp turns. The sound is loud enough to be distracting and I'm worried it might cause some damage to the car's components if left unchecked.