I incline in the wrong direction

a voice cries faint as in a dream
from the belly
of the wall

Is "A voice cries faint as in a dream" an example of a metaphor? if so, why?

No, there's a simile there. The word "as" indicates there's a simile.

http://knowgramming.com/metaphors/metaphor_and_simile_difference.htm

Yes, "A voice cries faint as in a dream" is an example of a metaphor. A metaphor is a figure of speech that directly compares two unrelated things, suggesting a resemblance or an analogy between them. In this case, the phrase "a voice cries faint as in a dream" is comparing the sound of a voice to the way it would sound in a dream. It suggests that the voice is feeble, weak, or distant, similar to how sounds can be perceived in a dream. The metaphor creates a vivid and imaginative image in the reader's mind, adding depth and emotion to the description.