If a WAV file is in question, cue points can striped or added via the current version Goldwave, and a new copy of the WAV file will be needed, which I can provide for you, should you name the original file.
If you want to make a looping wave, any cue point at the start of the file will have that effect. Similarly, needs to be saved as a new WAV, if it's an existing one.
The cue points of existing files are as they should be for their intended use, changing them will result in sounds looping when they should not, or the reservse, or "channel confusion", so any altered waves must be saved as new files.
MP3's loop until their time is up, however. There is no avoiding that, save to give them a very lengthy repeat time (eg. "9999") or playing some other MP3 file, such as "stop.mp3".
We've long used the latest retail version of GoldWave.
(Tools->Cue Points..., Delete/New..., Save As.., PCM signed, mono, 8-16bits, 8-22Khz.)
(44Khz is also possible, but causes issues due to the channel shift, and only 8-bit waves of 11Khz or less can be pitch changed reliably.)