Out and about this evening when I noticed quite a loud creaking noise when I brake. I've never heard it before.

When I got home I pressed the pedal with the engine off and the creaking noise seems to be from the servo area, its very loud the pedal pumps hard and goes down when the engine starts as normal. The noise stops when the pedal is hard.

Is there a spring that could do with some grease or something ? I haven't heard of this problem before has anyone else ?
TIA
Si