I've run across the same problem. Using .wav files recorded on Zoom H4N, I note that the recorded files, when playing from an external Seagate USB 3.0 drive, do the bizarre playback thing when put on the Vegas 13 timeline (also Vegas 12).
However, the exact same file, when put on my desktop and then dropped on the timeline, work perfectly fine in Vegas. In fact, I find the same file plays fine from some external USB 3.0 drives, but not all of them; it even plays on the timeline fine from the original SD card.
One workaround I've used is to open the audio file in Adobe Audition (might also work in Sound Forge, but haven't tried it) and then save it back to either the same file name or do a save as. Either way solves the problem - drop it back on the timeline and it plays/looks fine.
The problematic files that won't play on the Vegas 12/13 timeline DO play fine in QT, Windows Media player, VLC, etc - just not Vegas. So I agree - probably some Vegas issue.