Anyone else heard weird knocking coming from inside walls of old houses?

Not really my usual corner of the site (more of an abduction guy) but yeah I've had this at my nan's old place in Hereford. Three knocks, pause, three knocks again. Drove everyone mad for weeks.

Most likely explanation is thermal expansion in old timber frames, pipes contracting at night, that kind of thing. Old houses move around a lot more than people realise. But the rhythm of it is what gets you isn't it, when it sounds too deliberate to be random settling.

Anyone had it investigated properly? Like actually ruled out the mundane stuff before jumping to conclusions? Curious what people found when they actually pulled walls apart or got a plumber in.

@BristolCrow the triple knock pattern is genuinely one of the more consistent things that comes up across different traditions. Some researchers link it to a kind of mimicry - which is interesting because you see the same thing in certain abduction accounts where experiencers report knocking before contact events.

Worth noting whether it always happened at the same time of night. Thermal expansion in old houses can do rhythmic knocking but it doesn't tend to cluster in threes like that, it's usually more random. Three is deliberate feeling.

What was the house's history like? Age, previous occupants, anything unusual happen there before your nan moved in?