Star Trek Computers

On Star Trek, especially Next Generation, whenever anybody has any serious questions to work out on the ship computers, they give verbal commands and the computer talks back to them.

This would logically lead to a situation akin to sitting on a bus or in a store full of people talking on their cell phones--stray bits and pieces of conversation colliding to create a noisy, discordant background noise.

But when you enter the bridge or the engineering room, you don't hear a dozen muffled conversations, just the hum of machinery. So what the hell are people working on?