Lefty IS absolutely correct.
Improper lifting or ripping the line from the water creates a LOT of noise underwater.
I too, have spent some time diving and the advise to submerge one's head underwater and listening to a line being ripped is GOOD. Depending on conditions sound can be good (Dorado?) or sound can be detrimental (troutoids). It is for sure, that learning to be "soundless" would be QUITE advantageous as one could go from soundless to sound if desired, but NOT having the skill, would leave one no option but to be noisey.
One of my pet peeves is "slurping" anglers.
Spey casting anyone? VERY FEW spey casters have learned not to slurp.
.....lee s.