There are 3 cause of this issue:
1- Group loop on your connector
2- VGA cable or VGA output port issue
3- VGA chipset issue
But the highest posibble option usually is frist
To fix this issue
1 - Follow this article to break the ground loop on your monitor and laptop connectors
https://mrgnome.wordpress.com/2009/06/12/external-monitor-flicker-laptop-ground-loop-problem-solved/
2- TESTED ON UBUNTU: If the above solution cant help, try to install TLP and reboot your ubuntu, the noise will be gone. To install TLP, follow this article
http://linrunner.de/en/tlp/docs/tlp-linux-advanced-power-management.html
Good luck