Originally Posted by stinginrivers
Heard it as well on ruby horsethief. Drove me nuts trying to find the hole till I figured out what it was.
The kayakers on our trip showed me a cool trick, you put the paddle blade in the river and put your ear to the shaft or other blade and you can hear the same sound.
I've had the same occur in canoes... I was once told that the noise is created because of the velocity profile of the river being faster at the surface and slower at the bottom of the river due to frictional forces.
The theory was that the current of the river is different at the draft line and the bottom of the boat. The water makes the popping sound you described because when you are floating on the top of the water surface which is faster than the water at the bottom of the boat. This makes the water speed relative to the water surface different than at a the bottom of your boat. Kind of like how an air plain has both ground speed and air speed.
maybe that's it? or maybe i'm totally incorrect but I bought into the BS and sounds like a good explanation.