Harry didn't ignore it. It always comes and goes sometimes.
Hermione said that it was some form of PTSD he was suffering. He only pretended that counseling helped to save her worries. She already had enough problems to worry about.
Ginny understood and let Hermione pretend to be right. Sometimes, during the nights she would ask him if he was getting scared. She never accused him of being paranoid. Still, She offers to hold him during the nights if he wants her to.
Ron was always there to listen if Harry promised to buy the drinks. They both talk for hours to end, not coming to a conclusion or offering each other solutions. But they would talk, always lending their ears to their best friend.
George. Harry swore that George heard it too. That one time when he looked up with a smile on his face. He has started to smile more often. It suited him, Harry thought.
Finally, after years of just hearing the song alone, Harry saw him. A sight to sore eyes, he appeared just as majestic as he last saw him. Well, maybe a bit smaller in size but consider his new companion, it's good enough.
Fawkes, the phoenix perched upon Albus's shoulder, just as it was always meant to be.