I notice a strange crackle while booting my new Dell Latitude E7470 with a fresh ubuntu on it. It happens twice on every boot. Once before entering the password and once after successful login.

I found a solution by toying around with the alsamixer.

For me the solution is to disable the loopback channel.

Start alsamixer with this command:
alsamixer -c0

• Naviagate to the Loopback channel rightmost with arrow-key
• Disable the Channel by pressing the arrow-down-key once
• Save and quit the alsamixer with ESC

alsamixer

After that you need to reboot. The crackle is gone.

Have fun…