Symbolism, Imagery, Allegory
Did you notice that whenever time stands still—literally—music isn't too far off? Check out the first time this happens in the book:
He was woken by music. It beckoned him, lilting and insistent; delicate music, played by delicate instruments that he could not identify, with one rippling, bell-like phrase running through it in a gold thread of delight. There was in this music so much of the deepest enchantment of all his dreams and imaginings that he woke smiling in pure happiness at the sound. (2.1)
Let's take a close look at this passage. This music wakes Will up, but it doesn't disturb anyone else in his house—he even calls to Robin, but gets no response. This is because Will is an Old One, though he doesn't know it yet; he is metaphorically waking up to his magic here.
Notice the word "insistent." The music subtly lets us know that what's happening to Will here isn't something he can just avoid by, say, rolling over and falling back asleep; he's been pulled along. Notice also the word "enchantment." While at first glance it might sound like Will is being put under a spell, really it's more like he's stepping into his own enchanting powers—he possesses magic just as much as magic possesses him (you know, since he doesn't decide to become an Old One—it's his destiny). It's also important to note that Will feels "pure happiness at the sound." In other words, this music doesn't herald the arrival of bad news.
The melody encourages Will to leave his house and find the doors, which leads him to Merriman. It seems like any time this Old One's magic is activated, there's music around, and before too long, Will figures this out. He listens for the music and takes it as a comforting sign that Merriman is close by, ready to help if he needs it. That's music to his ears, terrible pun totally intended.