MTS files are supported.
The audio issue appears to be intermittent, and hasn't shown up in v13.28 here. Try Dangenfreak's 'auto-normalize' suggestion.
Also try this, after closing Videopad. Using Windows Explorer (the file manager), delete all files in these folders. Then install this release.
"C:\Program Files (x86)\NCH Software\Components" or a similar path without the (x86).
"C:\Users\Howard\AppData\Roaming\NCH Software\Components"
Share a file or two that doesn't load correctly...
Upload the file/s to a free server, such as Google Drive or MS OneDrive, get a shared (public) link, copy the link and paste it here or to me in a Private Message via the mail envelope in the top-right corner of this forum. When using Google Drive, if necessary change "restricted" to "anyone with link can view."