Like Andy said DON'T WAIT!AND TO ADD;>>>My Spit did the same thing at one time KLUNK KLUNK,Until i found the RIGHT REAR AXEL SHAFT BEARING & CAGE HAD DISINTIGRATED.So i went the common sense route & entirely replaced the whole right rear axel assembly including the axel,bearings,ALL THE u-joints,& while at the same time i replaced the leaf spring.NO MORE NOISE & NOW more piece of mind.I can even hear gas sloushing in the gas tank now at 30mph.OH!ONE OTHER THING while your at it RE-TORQUE ALL the flange nuts on the drive shaft front & back they have a tendency to work loose.Buy HIGH QUALITY U-JOINT's some u-joints are made in India or China which are junk.British are the best(MOSS,or TRF,or Rimmer Bros.
Ken......& WhiteLightning...1500 Spitfire