iMac Weird Boot Up Pattern

[timsalmon]

I haven't noticed this before and wonder if I should be concerned. It seemed to start after I used Bootcamp, installed Windows 7, changed my mind and removed it again. Then reinstalled OSX (for other non-related issues). It seems to be a 'streaky' kind of 'marble' pattern during the boot process which goes away when it's all fired up. Any ideas?

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...actually it's there all the time. Just need the right level of brightness to see it.

 

[JustMartin]

Looks like dust to me. Suspect the boot camp thing is a coincidence. Lots of notes out ther about cleaning inside iMacs.

 

[timsalmon]

Many thanks...

...will investigate further though if that's all it is and won't effect functionality *and* I find it hard to see routinely anyway, maybe I'll ignore! Response appreciated