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Why are some sounds so unpleasant? - Through MRI scans, researchers have found that activity in the amygdala (the part of the brain responsible for emotions) increased when people were exposed to certain sounds.

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What happens in our brains - The study found that this activity of the amygdala then increases our perception of unpleasant sounds when compared with sounds we usually find soothing.

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Sound frequencies - The study found that the high-frequency range, between 2,000 and 5,000 Hz, was the most unpleasant for the human ear.

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The most annoying sounds in the world - Next are the 10 most unpleasant sounds you can listen to. Ready?

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10. Electric drill - We've all heard this one at some point. It seems to be even more annoying when somebody else is using it, right?

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9. Baby crying - The desperate cry of a baby triggers all sorts of emotional responses in us. Parents, and anyone who's ever been exposed to the sound of a crying baby, can relate.

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8. Squealing brakes on a bicycle - Think when you break and that high-pitch sound penetrates your eardrums like a sharp knife.

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7. Angle grinder - Yet another power tool on the list. Though the sound of this one is, apparently, even worse than the sound of a drill.

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6. Female scream - This might have something to do with how high-pitched a female scream can be.

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5. Nails on a chalkboard - And here's the classic nails on a chalkboard. If this sound doesn't send shivers down your spine, then try and do it yourself.

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4. Ruler on a bottle - Using a ruler against a bottle will produce a very unpleasant sound.

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3. Chalk on a chalkboard - For those who had these in classrooms, you know how annoying chalk on a chalkboard can sound.

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2. Fork on a glass - There is just something about rubbing metal on glass that produces such an unpleasant sound.

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1. Knife on a bottle - And here is the most unpleasant sound to the human ear: running a knife on a bottle. You can listen to it here.

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The most satisfying sounds in the world - On the flip side of the coin, there are sounds that are quite pleasant to the ear. Though further research is needed, here are some of the most satisfying sounds you can listen to.

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Baby laughing - Contrary to the sound of a crying baby, this one can be very soothing.

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Fire crackling - We've been gathering around fire since the dawn of time. There is something comforting about burning wood crackling.

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Rain - Whether it's hitting the roof while you're in bed, or splashing against the window while you sip on a hot drink, rain sounds great.

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Golf ball going in the hole - There is something pleasurable about the distinctive sound a ball makes when it falls into the hole.

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Walking over fresh snow - You know that crisp sound when you first walk on a fresh layer of snow. It's great!

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Bird singing - This sound is often associated with positive things, and there is a good reason for it. Most of us like to listen to birds singing.

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Applause - Not many sounds come close to the one made by people clapping. It's a very satisfying sound, especially if they're applauding you.

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Water flowing - Water is life and the sound of it flowing can be very relaxing indeed.

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Thunder - This one is surprisingly pleasant. Perhaps it's the sound frequencies, but humans like the sound of thunder.

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Cat purring - A cat purring sounds very warm and sweet, and we humans love it.

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Airplane 'ding' sound - When you land and the seat belt sign turns off and you hear a very satisfying 'ding' sound: freedom!

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Sound frequencies are at the base of which sounds we find pleasant and unpleasant - Find out how sound frequencies can heal you and save the planet here.

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