In retrospect, it was on DL, SLC-YYC. We took off and soon noticed a sound like a bowling ball rolling around in a car's trunk. Then we noticed periodic louder noises. Then we noticed that we weren't climbing very quickly. Then we noticed that we were turning around. And were back on the ground.

Turns out one of the baggage doors wasn't properly closed. When the engine on that side (I forget the type of aircraft, but it had rear-mounted engines) was running it sucked the door back, blocking the airflow. The engine would shut down. The door would then relax enough, bouncing around in the turbulence, to let in enough air for it to start again, after which it would shut down again, and start again, and ... you get the idea.

It all happened too quickly for me to be scared at the time. That happened later.

The Delta agents, faced with 100+ panicky people who wanted to get to Calgary, were so happy that I'd take Edmonton instead that they gave me a complementary upgrade. (This was before SGB. I doubt that would happen now.)