Vent Axia in celiling runs constantly!?

I live in a 3 storey townhouse and there is a vent axia fan/vent in the ceiling above the top stairs. I've never really taken much notice of it and and have no idea what it does. I never even know it had a motor etc but over the last few days it has been running almost constantly and emitting a very low frequency noise that you can "feel" - even f you can't hear it, all over the house.

Does anyone have any idea how I can stop this noise , and also what the fan is supposed to do? I don't want to cut the power off etc if its doing something important!!!

Please excuse my total lack of technical knowledge!
Any assistance would be greatly appreciated.

PS The fan comes out into my loft and was put in whn the house was built approx 8-9 years ago.