Judging by the title and the imagery, the speaker is sitting in the dark during a storm, perhaps with the power out, and hearing everything too closely. The clock's ticking, thunder, rain and a buzzing sound all run together until it is hard to tell which is which. The speaker seems to be lying near or under a bed, with a head that "roars," so the storm outside and the noise inside the mind blur into one.
The line breaks do a lot of the work. Words are chopped mid-way ("under- / neath," "tight- / ly"), so the poem itself seems to tick and stumble like a clock. Time and rain become the same thing: "drops hum," "tears," "drops fall / fall fall." That suggests the rain may also be crying, though the poem never says so outright.
The mood is anxious and tense, with a hint of sadness. The last lines, "seconds / between / the sound," leave us waiting in the gaps, unsure what comes next.