Pipes making a loud rattling sound

This sounds like a common problem we call water hammer. This can be caused by various different things but typically tends to be a warn washer vibrating in the seating of a ballcock, (usually in a toilet but more commonly in a cold water storage cistern). This can be easily rectified by replacing ballcock or offending washer, and if necessary adequately clipping/supporting pipe work. It's not dangerous to be in the house, however if the problem is left for a prolonged period, the vibrating can put a strain on joints and pipe work in the system, and eventually cause leaks.