When using the headset under Debian Jessie, there is a continuous current sound, whether or not the music is playing. Attempts to write option Snd-hda-intel model=asus-mode1 ~ asus-mode8 in/etc/modprobe.d/alsa-base.conf have not worked.
Later found a workround (Bug #1405691: alsa-tools):
1. Install Alsa-tools-gui: $ sudo apt-get install Alsa-tools-gui
2. Run Hdajackretask: $ hdajackretask
3. In the window that opens, select a codec choose Realtek ALC668.
4. Tick the show unconnected pins option. In the list on the left, locate the item with PIN ID 0x1a, tick Override, and then select internal speaker in the drop-down list.
5. Apply Now and install boot override.
6. Restart.
This workround was originally used to solve the subwoofer problem, but following these steps can also solve the headphone current sound problem, a bit strange. In short, the headphone's current sound finally disappeared.
N551JW solve the headphone current sound problem in Linux