Strange knocking coming from inside my walls every night at 3am — finally caught it on video

Classic 3am window, that's basically the poltergeist's preferred office hours isn't it. Would love to see the video - have you managed to rule out pipes yet because that's always the boring explanation people throw at you first. I investigated a property in Winchester last year that had almost identical knocking and it turned out to be completely isolated to one wall with zero plumbing behind it, surveyor was stumped. The pattern matters a lot too, is it random or does it follow any kind of rhythm? Residual activity tends to repeat in loops whereas intelligent haunting responds to stimulus, so try talking to it directly and see if the frequency changes. Would genuinely watch that footage on repeat, get it uploaded if you havent already.