What version of Premiere Elements and on what computer operating system is it running?
Broadly generalizing, I might expect this of the Elements Organizer 13 and the .m2ts file, but not the Premiere Elements 13 Editor.
So, more details on program, computer operating system, and video properties beyond file extension and other aspects of your workflow.
The answers will be in the details.
Looking forward to your follow up.
Well now it's Elements organizer 15, but I had the same problem with Elements Organizer 14 also. This time I could play back AVCHD files (m2t and MTS) with sound until I installed Photoshop Elements 15. Now I have no sound again. I can playback with sound just fine from Windows Explorer, but hot the PSE Organizer.