Hi all!
I have Dell Vostro 3550 laptop with core i3 and Ubuntu 12.04.1 installed. And there is some strange issue: continuous generation of keypress event which looks like "^@" symbols combination in console and causes graphical interface flickering (not entire display, but windows and cursor), but when external monitor is plugged everything changes dramatically: flickering stops and monitors start to turn off and on in various resolutions.
Experimentally I've found that this issue is caused by "Video Bus" input device:
$xinput --list --long
↳ Video Bus                               	id=8	[slave  keyboard (3)]
	This device is disabled
	Reporting 1 classes:
		Class originated from: 8. Type: XIKeyClass
		Keycodes supported: 248
When device is disabled by following command:
xinput set-prop 8 "Device Enabled" 0
everything becomes ok.

Here are some details:
$xinput --watch-props 8
Device 'Video Bus':
	Device Enabled (140):	0
	Coordinate Transformation Matrix (142):	1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
	Device Product ID (257):	0, 6
	Device Node (258):	"/dev/input/event7"
	Virtual Device (259):	1
$cat /proc/bus/input/devices
I: Bus=0019 Vendor=0000 Product=0006 Version=0000
N: Name="Video Bus"
P: Phys=LNXVIDEO/video/input0
S: Sysfs=/devices/LNXSYSTM:00/device:00/PNP0A08:00/device:19/LNXVIDEO:00/input/input7
U: Uniq=
H: Handlers=kbd event7 
B: EV=3
B: KEY=3e000b 0 0 0 0 0 0 0
$lsinput -v
   bustype : BUS_HOST
   vendor  : 0x0
   product : 0x6
   version : 0
   name    : "Video Bus"
   phys    : "LNXVIDEO/video/input0"
   bits ev : EV_SYN EV_KEY