h-rattle,

bubbles do make sound; just ask a submariner; the sound may be in the ultrasound range but with the right ears you may pick up some sell or buy signals; the frequencies depend on many factors and could be characteristics for even individual ships or whatever

in the 'old' days experienced operators often could 'listen' to chemical reactos to determine their state of health, similar to a doctor listening to your chest.

so don't underestimate bubble sounds