Continuity mistake: When they initially pull into the handicapped parking space, George is driving a large yellow Cadillac. When they return to see the car destroyed, it is now a much smaller blue car.
Continuity mistake: When Kramer enters Jerry's apartment, he closes the door. In the next shot, the door is wide open. A few shots later, George opens the door, which was closed when he entered.
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