Flashing black pixels in games background, what could it be?

[Lord_Tibor]

It happened this on my AES, with super sidekicks and fatal fury 2 only... what could it be? are the games supposed to have those glitches?
I have a rev 1 (with daughter board) euro console

 

[HeavyMachineGoob]

Either a dirty connection or inadequate power supply.