The rotors are fairly quiet, I’d say similar sound to a computer fan, a low wooshing sound, nothing like the high pitched buzz of a drone. They can get louder if they get corrosion inside, so running in freshwater after salt water dives is a must.
Fish seem to react differently some will bolt but it seems like most don’t seem to mind the Trident, even down deep with the lights on, I’m suprised how tolerant they are of it.
Depending what kind of behavioral studies you are doing a fixed camera may be better? Just a thought.
I have not swam with a Trident in the water or have a Blue Robotics to compare noise to.