Plenty of technical info here, moggie ...............
http://www.nuaire.co.uk/product/genieb
I guess it's for background trickle ventilation, to keep the room free of condensation.
It shouldn't make that noise, obviously faulty. It should be replaced by the builder.
In the meantime, all such fans are supplied with a switched live(pull cord), and a permanent live (no switching). Their should be an isolator switch somewhere (often just outside the room) ..... this will turn both lives and neutral off.