Pulsing Brakes
This one is definitely automotive in nature.
Here we go.
Years ago, a guy walked into the shop with a Volvo. The guy complains of a strong pulsing in his brake pedal when he applies the brakes.
The mechanic looks over the car and finds that the front disc brake rotors are warped.
The mechanic installs new ones and sends the fellow off on his way.
Well, 5000 miles later, the same car owner comes back to the shop and complains that the pulsing is back.
The mechanic is suspicious because he knows his work on the car was excellent.
The mechanic asks the owner a few questions to try to get to the bottom of the issue.
Do you ride the brake? Have you tightened your lug nuts with a high powered air wrench? Have you bought new tires?
The owner answers no to all these questions.
The mechanic is at a loss and replaces the warped rotors again.
After another 1000 miles, the guy comes back with the exact same problem.
This time, the mechanic asks straight up, what the heck he's doing to the car that could be causing this problem, knowing that there's nothing wrong with the parts and nothing wrong with the installation. This should not be happening.
And the fellow says, "I don't know. I go on a lot of long car trips, and it's always the day after I arrive home from these trips that I start feeling the pulsing. But it never happens during the long time, only on the day after."
The mechanic asks him one question. And then he knows the answer to the puzzle.
What question did the mechanic ask?