Zanussi IZ16, clunking noise on spin but low vibrations?

Our 7 year old IZ16 has recently become significantly more noisy during spin cycle with a disturbing clunking. Vibration levels through the floor are still very low. I have changed the brushes which were very near the end of their life (though I am not convinced I have tightened the screws securely). It almost seems like one of the concrete weights is not quite in the correct place. Any suggestions? Is it a case of new bearings and if so, is this something a reasonably intelligent (and handy!) person can do?