Rain is the whole scene here, but it quickly becomes more than weather. The poem begins with a single "Drop," then widens to "Drops," as if we're listening to a shower start up. The speaker lists where the water lands: the floor, the window sill, the shingles, the door, the tiles. Each place is close to home, so we feel the speaker sitting indoors, listening.
The verbs shift the mood. "Rolling" and "splatting" sound almost playful, but "bursting" and "tearing" are harsher, and by the end the rain is "numbing out the pain" and "hiding away the screams." The speaker seems to be dealing with something hurtful, and the noise of the rain offers cover. The poem doesn't say what the pain is, and that silence makes it feel heavier.
The mood is quiet, tense, and a little bleak, though the rain also feels like a strange kind of comfort, a sound loud enough to hide behind.