Why are my pipes noisy when heat/water is off?

When our heating is ON our pipes bang as they change from cold to hot which is probably pretty normal in a 1979 house, they’ve probably changed position since they were fitted and don’t have enough space. However, after 6 months living here, suddenly they’re a bit noisy at 11-12 at night when I’m trying to sleep - but haven’t been until 2 days ago. So why now? - Nothing has changed on the Hive setup - heating is off still (sept and temp 20c inside) - hot water is on 9-10am and 9-10pm daily - I checked the boiler at 11.15pm and everything was off and feeling the pipes they weren’t hot - I felt the radiators in our room, the hall and spare room by hand, all cold I have a new horizontal pressurised tank in the loft as of 4 months ago. The ONLY thing that’s changed in the last week was on Saturday (3 days ago) when I turned the 2 hot water valves off on the cylinder while I replaced a basin and put them both back on again after. Since then we’ve had plenty of showers or run hot water for things. I’m stumped on the logic of what it can be - does anyone know?