When powering a commandblock with a trapped chest, /playsound will sometimes play the sound when closing the chest as well as when opening the chest.

It also sounds like when you power it with - for instance - a lever, the sound plays twice simultaneously.

To illustrate, here is a video. I was able to reproduce this several times with the setup I show in the video. (CommandBlock output was disabled).

https://www.youtube.com/watch?v=p5DA3dq1TU8