Classic setup honestly. Attics are weird spaces, the acoustics in them can make small things sound massive so don't rule out something pretty mundane like a squirrel or a bird that's got in through a gap somewhere.
That said, I've had a few experiences in old buildings around Glastonbury where the noise turned out to be nothing explainable and the camera footage was just... odd. Not dramatic, just movement in the corner of frame that didn't make sense.
What kind of camera did you set up? Night vision or standard? And has the sound been consistent or does it come and go at certain times of night. Timing patterns tell you a lot, both for the mundane explanation and the less mundane one.
Genuinely curious to see the footage when you've had a chance to review it. Post it up even if you think its nothing, sometimes other people spot things you miss when you've been staring at the same clip for an hour.