Hello,

My new laptop has Stretch with Gnome3, on HP elitebook 840 p2.
It's been a few days since the brand-new installation, and I found that there's consistent level of background white noise when I use my headsets.
I tried with other earphones as well, but white noise level is same.
This noise is not probably due to the main board, because it increases when sound card module is loaded during boot procedure.. but maybe I'm wrong. :P
On my another laptop, which is different model and has Jessie with Gnome3, there was no such problem at all.

I first tried to turn-off mic boost in alsamixer, but I found that there's no mic boost options in my alsamixer.
Is there any solutions to fix background white noise? It's quite annoying, I can hear it even if I make a skype call, for instance.

Any comments or advices are welcome!

You said you checked the mic-boost options. Are you aware that you need to press the tab key to switch between outputs, inputs, and all mixers? The mic boost would usually only show up on second or third options.