Robert F. Kennedy Jr.'s distinctive "funny" voice is primarily due to a neurological condition called spasmodic dysphonia. This disorder causes involuntary spasms in the vocal cords, resulting in a raspy, strained, sometimes shaky, and quivering voice when he speaks. The effect creates a distinctive, gravelly timbre that adds a unique texture to his voice.

In addition to the neurological condition, RFK Jr.'s speech style includes a slow, measured pace with strategic pauses, varied intonation with melodic rises, and emotional expressiveness, which all contribute to how his voice sounds. His voice has a certain raspy and emotive quality that enhances his storytelling and oratory style, making his speeches compelling though distinctive.

In summary, RFK Jr.'s "funny" voice comes from spasmodic dysphonia and his intentional speaking style that emphasizes rhythm, emotional expression, and vocal variety.