Hi @lunarminer
I’ve been testing a Hydrophone from Acbotics, and have seen this spectrogram when driving around with a BlueBoat. While this is a different prop than you may be using, the frequencies should at least be similar.
It’s worth noting that if your AUV is particularly low-drag, it would benefit from ditching the thruster nozzles! These maximize force, but at the expense of drag, and so for low drag vehicles that cruise at high speeds (1 m/s +, vs. an ROV) they are likely slowing you down!
From riding around on a T500 based DPV, the noise doesn’t seem to bother dolphins (see first video), and the electrical signals in the water may even tend to attract sharks?