It was quiet at Hogwarts.
In the muggle world, there was always noise. Cars vroom-ing, the refrigerator buzzing, the heater whirring, the television chattering, people yelling, Dudley's video games screaming, and a plethora of other sounds clamoring at his ears day and night until someone who wasn't used to it would have gone mad. But Harry was used to it, and so he barely even noticed.
Most of all, there was music. In the supermarket and shops, there was music playing softly overhead. In the elevators, there was elevator music. At the Dursley's, Dudley played music on his boom-box, or the telly had theme music, and even the video games had music in the background.
There was no music at Hogwarts. Oh, there was that lovely little piece on the first day, but after that, the only music was what one made for oneself; and most people were far too shy to make their own music. Someone might hear, after all.
There was no music at Hogwarts.
For the first few days, it didn't really bother him. He hadn't noticed the music in the first place, so why would he notice it missing? Then, after a day or two, when the excitement began to wear off, he started feeling itchy and squirmy and wrong. There was something missing, and he didn't know what it was.
He slept poorly. He didn't eat enough- not that he ever had, really. He was slowly going insane from missing the noise that would have driven most wizard-born insane- and he didn't even know what was wrong. He threw himself into the mysteries he found, thinking that they were the problem, that if he could solve them, fix things, it would all be better. He did. It wasn't better.
On Christmas of Harry's first year, Hagrid gave him a flute. If Harry had known what was wrong, he might have learned to play it; but he didn't.
He got used to it. Human beings are very adaptable creatures. And when he went to the Dursley's each summer, they seemed louder and louder and louder until he thought he would go mad if they didn't just shut up because day and night day and night there was noise noise noise!
But even so, when he heard someone playing music- even badly- Harry couldn't help but sit and listen, glad for it. Because there was no music at Hogwarts, and he needed music.
So it happened that, eventually, he learned to play that flute. So it happened that he learned to sing. So it happened that he got Ginny to teach him the lullabies that she sang to their children. So it happened that he bought a Wizarding Wireless, even though they were so expensive. So it happened that he had his children (and himself) take music lessons. So it happened that he filled his home with music, without even knowing what he was doing. So it happened that he gave a grant to Hogwarts, to be used for music classes. So it happened that, when James started school, he gleefully used his talent for singing as an excuse to show off. So it happened that other kids started to sing. So it happened that...
There was music at Hogwarts.