In this context, "grate" means that the sound of Al sobbing is causing discomfort or irritation, as if the sound is harsh or unpleasant. It's a figurative use of the word to convey the emotional impact of Al's sobbing on the narrator. It means that the sound of Al sobbing is so distressing or unsettling that it feels uncomfortable or painful for the narrator. The word "grate" is used to describe the emotional reaction to the sound, as if it's causing a sharp or unpleasant sensation in the narrator's throat.

In the sentence, "I almost feel the sound grate in my own throat," the word "grate" is used metaphorically to convey a sense of discomfort or irritation. In this context, it suggests that the sound of Al sobbing is so distressing or unpleasant that it feels as though it's causing discomfort or a similar sensation in the speaker's own throat. It's a way of describing the emotional impact of Al's sobbing on the speaker.