Noisy cold water pipe at night?

It may be water hammer. This is caused by the ball valve in the loft tank vibrating and causing a standing wave in the main supply pipe. A temporary solution is to get a large polythene bag, partly blow it up so it makes a floppy cushion, seal it and put it under the float in the loft tank. If that solves the problem, you need a new ball valve with the float adjusted so it's not in the middle of the tank.