Name that Noise

When I was in college, I had my very own house painting business. It was great, because most of the jobs were in the small town where I lived, and if it rained, I got to sleep in.

Near the end of the summer, I got a job 20 miles away. When I drove to the new job on the interstate, my elderly Oldsmobile Delta 88 began howling loudly. The volume and pitch of the noise were directly related to the speed I drove. I pulled over, I opened the hood and looked around, but I couldn’t find anything obviously wrong. So, I drove to the job and spent the day scraping, with a heavy heart.

When I drove home that night, though, the noise had disappeared. And it didn’t come back during the 10 days it took to paint the house. So naturally, I forgot about it.

The day I finished the job, I loaded up my equipment and headed for home with a fat wallet. As soon as I hit the Interstate, the howling returned. I drove home with a heavy heart, and visions of my paycheck being sucked out by the transmission repair shop. When I finished unloading my equipment, I realized what the problem was. Five minutes later, I had the problem solved without opening the hood, or turning a wrench.”

What was causing the problem?