Strange graphic artefacts on Ubuntu guest

[Dom]

I'm running an Ubuntu guest with XFCE on a Mountain Lion host (on a Macbook Air from a few generations back). Guest additions for 4.2.10 are installed, but the VirtualBox version running is 4.2.12. Strange artefacts appear on my screen for no apparent reason. Since I can't post screenshots (yet), here's what's happening: there's a row of equally spaced '=' symbols and multiple black lines running across the top of the screen, where the 'File Edit ...' line would be on a maximised app. This happens regardless of whether the guest is in fullscreen, or in a resizable window.

I've tried enabling and disabling both the 2D and 3D acceleration in VirtualBox, and running XFCE with and without the native compositor. I've also tried allocating different amounts of video memory to the machine. While it appears that some of my steps mitigated the amount of artefacts, some still remain and they're really annoying. Does anyone have any experience with this?

Any help would be appreciated.

[loukingjr]

I've never seen anything like that. As a guess, the guest has a problem. You shouldn't enable 2D for a Linux guest btw. You could try installing the matching guest additions.

[Dom]

I'll post pictures tomorrow, when the discussion board grants me the right. Later today I'll install another guest and see if the problem remains. Thanks for the tip.

Edit: I installed another guest system and there are no artifacts. I think I'll stick with this one. Thanks for pointing me in the right direction.

[loukingjr]

glad to help. you should mark your post as solved btw.