Right, before everyone piles in with ". It's definitely a portal entity" - let's actually work through this methodically.
First, rule out the mundane:
Thermal expansion in pipes and joists is incredibly consistent with timing. Central heating systems cycling on/off at the same time each night will produce rhythmic knocking that sounds deliberate. What's your boiler schedule set to? Any radiators on that wall?
Also - rodents. Specifically rats in cavity walls follow surprisingly regimented patterns tied to feeding cycles.
If you've genuinely eliminated those:
The regularity is actually what makes this interesting from a paranormal standpoint. Random poltergeist activity is common. Patterned activity is rarer and worth documenting properly.
Set up a temperature/humidity logger alongside your audio recording - I use a Govee Bluetooth sensor paired with my Zoom H5 for EVP sessions. Sudden drops correlating with the knocking events would be significant data.
What's the pattern specifically? Sequences of three are practically cliché at this point, but if you're getting something more complex - prime numbers, irregular intervals - that warrants a different conversation entirely.
Also worth noting: what's the history of the property? Essex myself, and half the Victorian terraces here have enough structural quirks to mimic genuine phenomena convincingly.
Document everything with timestamps before drawing conclusions. What does the pattern actually sound like?