Trivia: When Jerry and Elaine discuss how evil Newman is, Elaine comments "Maybe he's an enigma, a mystery wrapped in a riddle." This quote from Winston Churchill was referenced in JFK (1991), which featured Newman actor Wayne Knight.
Trivia: In the very beginning of the episode the person wearing the cape is none other than co-creator Larry David.
Trivia: The end scene on the bus, when Kramer tells Jerry he's falling apart is a tribute to the film, "Midnight Cowboy" where Ratso tells Joe Buck he's falling apart. Joe Buck was played by Jon Voight, who appears in this episode.
Answer: Composer Jonathan Wolff used a synthesizer, although in seasons 7-9, a real bass is used in addition. Wolff also recorded himself making hundreds of mouth noises, pops, and slaps to add to the synthesized bass licks so that each episode has a different theme. The only real "back-story" is Jerry Seinfeld was having trouble coming up with a theme song and talked to a friend who happened to know Wolff. They wanted to avoid that cheesy late 80's sit-com theme song and Wolff came up with what we enjoy now. Jonathan Wolff has also talked about this further in interviews, recently Reed Dunela interviewed him, so for a fuller account of his story; check out "The Wolff of 116th street".
Bishop73