Companion makes a buzzing sound.

[octaviars]

It's the small ferrites inside the PSU. It's been discussed on this site multiple times and there even is/was a support article about it on the Devialet website.

I have tried to find it on Devialet site but can not do that......

Think this is what they wrote, found it in another thread. 

Although there are no moving parts inside a Devialet, you may hear in some cases an extremely soft noise in stand-by. There is absolutely nothing to worry about. It is caused by the vibration of some ferrite elements in the power supply. The level of this extremely low noise varies from unit to unit. Again, there is absolutely nothing to worry about.

Got a answer from Devialet today and they wanted me to record the sound and send it to them but my companions noise is so faint that it is hard to seperate it from the noise in the background.