I have an early 2011 Macbook Pro. I'm running a Dell 2407 monitor using a VGA adapter and I get intermittent wavy lines on the external display. If I open the display menu on the monitor itself while the problem happens, the overlaid menu is not 'waving'. If I adjust the pixel clock on the monitor while the wavy lines are there, this temporarily resolves the problem

I'm using VGA as the DVI connection had other issues - intermittent noise / snow. I will probably replace the Macbook later this year and maybe even upgrade to a new thunderbolt display but in the meantime, this is incredibly annoying.

This video shows the wavy lines I'm seeing (but this was not uploaded by me) - http://www.youtube.com/watch?v=yEyUk6S07iQ

I've plugged the monitor into a completely separate power source and can't identify any other source of interference.

I'm running OSX 10.8.2 Mountain Lion. The display adapter is an official apple one.

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    Is the VGA cable captive on the monitor end? – Thorgrim Feb 6 '13 at 21:58
  • @Thorgrim not sure what that means? – codecowboy Feb 7 '13 at 10:57
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    Can the VGA cable be unattached from where it connects to the monitor? Captive in this case means "cannot be removed". – Thorgrim Feb 7 '13 at 14:44
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    It can be removed yes. I have also tried a different cable. – codecowboy Feb 7 '13 at 15:49
  • My guess would still be the cable. Did either of the VGA cables have attached magnets? The magnets can prevent the cable from picking up external signals like an antenna. See Ferrite Bead, en.wikipedia.org/wiki/Ferrite_bead for an explanation. – Thorgrim Feb 7 '13 at 22:56

VGA cables are generally not designed for the high bandwidth required of large, digital displays, so it wouldn't surprise me if this is a cable issue that would be present in a variety of cables. I had similar issues with a KVM adapter. (If you're using a KVM adapter, then the KVM itself is probably the problem.)

One thing to try would be to lower the refresh rate on the monitor to the lowest setting the Mac will allow and see if that solves the problem.

Better would be to get the DVI cable working, but again the intermittent noise/snow points to a bandwidth limitation of the cable (or KVM adapter).


Replacing the power cable of the monitor is one possible solution, assuming the cable is the cause. There have been multiple instances of various Dell Monitor/Power Cable combos that have caused everything from strange output to jumpy mouses! This is inconsistent and can sometimes happen from even just certain positions of the cable.

Worked for a friend, and other on the net.


Maybe a DSL modem or DSL cable, or the DSL socket. Or a microwave oven.

Try in an empty room, in another house… to see whether the problem is specific to your environment.

  • 1
    I did try it in a different house and the interference was significantly less but I have experienced the problem in two different properties. I don't have a DSL modem or router in the room. Presumably a microwave would only cause interference while it is on? If so, its not that. – codecowboy Oct 19 '13 at 9:48

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