Audio Becomes Slower When Saved

We're having a strange, intermittant problem.

Audio is recorded into a multitrack session without issue. We listen back to it to confirm everything is fine.

But, once it's saved, the audio becomes slowed down. The actual file length becomes longer and the audio becomes very slow and crackly. The is true for playback in Audition and other programs.

As I said, it's intermittant. The studio is used for class work, so 10-12 students will use it consecutively and 1-2 will have this problem. We can't figure out any rhyme or reason.

Help!