Factual error: The Devils-Rangers game is at Madison Square Garden, but when the Devils score, a siren goes off. That would only occur in the event of a Rangers goal.
Character mistake: George makes a big deal about wanting to say "I love you" to the girl he's dating and says he's never said it to a girl, just a dog once, and he wants to say it just once. But in s02e01, "The Ex-Girlfriend", George tells Jerry he had to say "I love you" to Marlene when she told him she loves him.
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