[Joe Marvelly]

I realise this is a really late response but hopefully this answer will help anyone else who’s having the same problem!

Sounds like the original audio file is of a different sample rate to the exported audio. Check the properties of the original audio file (Right click and select properties) and the sample rate will probably be either 44100Hz or 48000Hz. When exporting check the audio settings and make sure you set the sample rate to the same rate (44100 or 48000) as your audio file.

Here are the effects of getting the sample rate wrong:

Original audio – 44100Hz (44.1kHz, CD Quality)
Exported Audio – 48000Hz (48kHz, Pro Video quality)
Result: Exported audio is faster than the original and slightly higher pitched

Original audio – 48000Hz (48kHz, Pro Video quality)
Exported Audio – 44100Hz (44.1kHz, CD Quality)
Result: Exported audio is slower than the original and slightly lower pitched

What you should do is:

If your original audio is 44100Hz:
Original audio – 44100Hz
Exported audio – 44100Hz
Result – accurate playback

or your original audio is 48000Hz:

Original audio – 48000Hz
Exported audio – 48000Hz
Result – accurate playback

Basically sample rate for audio is like the frame rate for video! If you have 10 frames for every second (fps) but play back 20fps the video will play back twice as fast as it was filmed! Hope this helps!