Hau,
Yep, yep. I will bang on the rocks on the bottom at times to attract Ling-cods in. Throwing the anchor off the boat and noise hitting the bottom works too. Usually something there when I follow the rope down to check placement. I always check the anchor with a gun loaded.
I brought this up, since there was limited chatter on it. The speed of sound in Water is so much faster than in Air, thought it would good for fellow spear-o's to think about it. 5000 ft/sec is smoking fast.
The sound can also be a positive as another thought. Any time I was hunting on Scuba, kind-a felt like I was hunting with a loud chainsaw on my back from the noise of the regulator.
The Speed variation based on Water Temperature was a something I forgot about from School days.
% wise, not really a factor, but interesting still.
Here is a reference with nice graphs.