Making note of interval timings with a stopwatch can show whether it really is random.
Disconnect all
batteries &
shore power and if it stops check individual items.
Bilge pumps, level switches, gas detector, log impeller,
depth transducer, ultrasonic antifouler - everything.
If you're moving or the water's moving maybe something's caught up on the
hull and fluttering in the flow?
Something like a marble rolling around in the
bilge?
I didn't even know there were noisy little fishies
Except the ones sizzling in my frying pan.