It looks like the little 'shock dampeners' (silicon- or rubber stuff?) got defective and my advise is to visit the repairshop.

Oh I've seen other 'defects':
Coins that slipped in (they can click)
Sticky sirup (you get this when Coca-Cola dries) that came in and glued the keys in down-position or created a sloooooow moving key.

Roel