Trimming audio source in Adobe Premiere
Adobe Premiere is Non-linear editing application. Any changes made in it don't have any influence on footage on your hard drive. Not audio, not video.

It is feature, which prevent damaging footage files.

It is based on trimming, not cutting. However, if you really want it, you can trim your audio, export it from Premiere, and then import back. But I can't find any reason, why you can need that.