I have a dirty secret: I am a dedicated Car Talk listener, and have been, since I bought my first car in 2006.
Every once in a while I like to imagine what it would be like to be on Car Talk as a caller.
Due to the fact that car noises do not puzzle me anymore, I don't really have a good excuse to call Click and Clack. Well then, I'd have to make something up!
I figure the call would go something like this.
Ray: "Hello, you're on Car Talk!"
Yours truly: "Ohai, this is Alex from San Jose. I have a 1990 white Mazda Miata, and sometimes it makes this loud BAM! noise from underneath the car."
Ray: "Is it a metallic noise?"
Me: "No, it's kind of like if someone whacks the underside of my car with a rubber mallet."
Tom: "Can you make that noise again?"
Me (happy to oblige): "BAM!"
Ray: "And it comes from underneath the car?"
Me: "Yes, kinda like from the wheel wells."
Ray: "All four at once?"
Me: "No, one, then another... but I think all four corners do that."
Tom: "When does the noise usually happen? Right away, or after you've been driving for a while?"
Me: "It usually is after I have been driving for a while. Like five to ten miles. Sooner when the weather is hot."
Ray: "Do you need to be going fast for the car to make the noise?"
Me: "Yes. Definitely over 70 miles an hour."
The hosts would hem and haw, and try to gain some time by asking more questions.
Tom: "So you said your car was red?"
Ray: "No, she said it was white!"
Tom: "You haven't got a clue, have you?"
Ray (to his brother): "Do you? (Then to me) Do you park your car in the street?"
Me: "No, I always park it in the garage."
Tom: "How many miles do you think you drive the car every month?"
Me: "No more than 200. Mostly on weekends."
Ray: "So when would you say are you most likely to hear the noise?"
Me (finally spilling the beans): "I'd say, at the end of a straightaway, like when I'm approaching Turn One at Thunderhill. Could it be the tire worms?" 
I don't see how this could possibly go wrong.
 Tire worms are worm-like pieces of melted rubber that accumulate around the circumference of the tire as the car slips a bit in corners. When you get to a straight and gather speed, the centrifugal force of the rotating tire will make some of them fly off and hit the underside of the car with that typical Bam! sound. The longest worm I saw stuck to my car was about 7 inches long and a good 1/4 of an inch thick.