Personally I like the water sound, and in fact I wake up at night now when I don't hear it, and know that there's a problem with one of my tanks. The fire bellies climb right on top of theirs and sit, so I can't imagine the sound bothers them much. Submerging is one solution if it bothers you, adjusting flow rate on some filters is another, and the third is to create a gentle slope. I use a fake rounded log in one of my tanks which gently guides the water where I want it to go.