[ubuntu] ATI display flicker

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http://ubuntuforums.org – I have had 3 ATI radeon cards now & always had display flicker with Ubuntu. I mostly use windows 7 and have to use Linux for my open source work (not gaming). I used to get round the problem by using Ubuntu in a virtual machine, but would like to use it native. I have just bought a new graphics card (XFX HD 6450) on Dell U2412M & once again display flicker (graphics signal NOT monitor) This is all the same hardware with DVI or VGA, 3 monitors all Dell U2412M @ 1920x1200, with / without proprietary FGLRX drivers, only 1 monitor attached, all produce flicker on Ubuntu & not on wi (Hardware)