Cheese

What does this mean? what can be done to cure it? The unit is a sony MZ-R909, i have been offered it for pittance but i'd like to know whats wrong with it, worth having?

has anyone had use of one of these or it's NetMD brother, the 250? I will be buying a new recorder in 2 or 3 months and this model catches my eye. i want tgo know how good quality, loud and freindly it is thanks!