electrical bang

About a month ago, I was in one of the office wings of the building that I work at. Went out the fire exit to enter the internal fire-escape stairwell of the wing that I was in to grab some network cables that were in a box that I needed (box of cables was in stairwell). On coming back into...

My grandparents live a bungalow with modern central heating that has a economy 7/dual tariff meter that according to them is making a loudish bang sound when it switches over at night and in the morning. Note that they do not have any storage heaters or any other high night time loads and only...