How does Roderick react to the sound coming from the house?

From the text:

No sooner had these syllables passed my lips, than — as if a shield of brass had indeed, at the moment, fallen heavily upon a floor of silver — I became aware of a distinct, hollow, metallic, and clangorous, yet apparently muffled reverberation. Completely unnerved, I started convulsively to my feet; but the measured rocking movement of Usher was undisturbed. I rushed to the chair in which he sat. His eyes were bent fixedly before him, and throughout his whole countenance there reigned a more than stony rigidity. But, as I laid my hand upon his shoulder, there came a strong shudder over his frame; a sickly smile quivered about his lips; and I saw that he spoke in a low, hurried, and gibbering murmur, as if unconscious of my presence. Bending closely over his person, I at length drank in the hideous import of his words.