Honestly this happens to me constantly in my Newcastle terrace and I've gone back and forth on it for years. Old houses are genuinely noisy - thermal expansion, joists creaking, the whole lot - but there's a specific quality to footstep sounds that's hard to dismiss as purely mechanical.
What I'd ask is: does it have a rhythm? Because random settling tends to be irregular. Actual footstep-pattern sounds have a cadence, a weight distribution. That's the bit that gets me every time.
I've got a Zoom H5 recorder set up on my landing when things get active, and a couple of times I've caught sequences that are clearly not random creaking. Whether that's paranormal or some weird acoustic phenomenon bouncing from the street outside, I honestly can't say for certain.
Few questions that might help narrow it down:
What time does it happen? (Mine clusters around 2-4am which means nothing scientifically but is still annoying), Does it always start from the same step?, Any temperature drops beforehand?, Anyone else in the house react - pets especially?
Cats and dogs are brilliant early warning systems. My old cat used to track something up the stairs with her eyes before I ever heard anything, which is either compelling evidence or proof she was just daft.
Don't rule out mundane explanations yet, but don't dismiss it either. Keep a log with dates and times - patterns matter more than individual incidents.
What's the house's age roughly? That changes things considerably.