A full revolution of the thruster isn’t the only source of oscillation, so sounds can be quite a bit higher pitched than just 66Hz. Since the Blue Robotics Low-Light Camera has a speaker built in, for a sense of the general ranges of sound you can expect I’d suggest listening to some dive logs, e.g. this one from @btrue has a video where the operating sounds are quite prominent.
If you need specific frequencies then I’d suggest either putting a sound measurement device (or phone with suitable app) near your computer speaker while playing a suitable clip, or you can download a video and extract the sound from it, and use some code to run a Fourier Transform on the sound waves and get a frequency histogram.
For actual amplitude data you’ll need to measure that, or find someone with the appropriate equipment who’s willing to do so for you. Are you after sound levels from inside or outside the water? (e.g. are you concerned about scaring fish/submarines, or annoying humans at the surface?).