誰かが大声で叫んだのが聞こえた。

who

indicates a question (sometimes rhetorical); or; whether or not; some- (e.g. something, someone); indicates doubt, uncertainty, etc.; emphatic prefix; suffix forming adjectives or adverbs; in that way

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

loud voice

indicates location of action; at; in; indicates time of action; indicates means of action; cause of effect; by; and then; so; indicates continuing action; indicates certainty, emphasis, etc.

to shout; to cry; to scream; to shriek; to yell; to exclaim; to clamor (for or against); to clamour (for or against)

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

to be heard; to be audible; to be said to be; to be reputed