Somehow, my MacBook Pro got squeezed in my briefcase and began to get hot and the fan was making an awful racket. I let everything cool off before opening the case. I'm not ready to part with this old Mac, so I ordered the fan, installed it with the help of the great wizards at ifixit.
She's purring like a happy kitten now!
Don't let someone else put your laptop in their overstuffed briefcase!