How to reproduce:
1. Open attached "repo_1030937" project
2. Open "Main Scene" scene
3. Enter Play mode
4. Listen to an audio clip
5. Go to assets folder and launch "test.mp4"
6. Compare original audio track with one played in the editor

Expected result: both audio tracks will sound the same
Actual result: Editor's audio track is choppy

Reproduced with: 5.6.6f1, 2017.1.3p3, 2017.2.2p4, 2017.4.2f1, 2018.1f2, 2018.2.0b2

Note: Probably because of overflow, but audio track's playback speed seems to vary