I wonder if you're remembering They're Made out of Meat by Terry Bisson. I read it in Bisson's anthology Bears Discover Fire. There's a copy on the East of the Web site here.
The story is two aliens discussing a newly discovered species (i.e. us). It is about the length you describe and does contain the reference to flaps of meat:
"They do, but what do you think is on the radio? Meat sounds. You know how when you slap or flap meat, it makes a noise? They talk by flapping their meat at each other. They can even sing by squirting air through their meat."
It doesn't specifically mention cars, but they do regard machines as superior and are incredulous that humans have apparently managed to make them:
"There's no doubt about it. We picked up several from different parts of the planet, took them aboard our recon vessels, and probed them all the way through. They're completely meat."
"That's impossible. What about the radio signals? The messages to the stars?"
"They use the radio waves to talk, but the signals don't come from them. The signals come from machines."
"So who made the machines? That's who we want to contact."
"They made the machines. That's what I'm trying to tell you. Meat made the machines."