Possibly collapsed suspension on the cartridge... Either that, or the weighting is set up wrongly and there isn't enough pressure.
Remove the cartridge and gently prod the stylus with your fingertip in the same manner as it would be hitting a record.. If it bounces back healthily, all is ok - but if it doesnt have much movement, it will need rebuilding or replacing.
Lee
BeoWorld - Everything Bang & Olufsen