Marks on screen

[Handle]

I have a 2009 24" iMac. Recently I noticed that when there is gray or light colors being displayed there are marks going across the screen. It looks like watermarks. There is no pattern, at first I thought the screen was just dirty but after looking closer I can see its definitely behind the glass.

Any idea what it is? I would assume burn-in but the pattern doesn't match anything I display.

 

[Apple fanboy]

I have a 2009 24" iMac. Recently I noticed that when there is gray or light colors being displayed there are marks going across the screen. It looks like watermarks. There is no pattern, at first I thought the screen was just dirty but after looking closer I can see its definitely behind the glass.

Any idea what it is? I would assume burn-in but the pattern doesn't match anything I display.

Dirt trapped beneath the glass was a common complaint on the older style iMacs. Could it be that? Usually described as a dark smudge.

 

[Handle]

It could be that, but it seemed to appear at once recently. You'd think dirt would build up slowly over time.

 

[Handle]

Now it seems to come and go

 

[Dreadnought]

Could it be the GPU is acting up? Please monitor the temps of especially your GPU. It could be it can't dissipate it's heat due to dust or it's dying. Try running your fans on maximum speed to blow out dust or open your iMac up and use compressed air to clean it.

 

[Handle]

How do I monitor the temps? Thanks.

 

[h9826790]

Is that only happen when the monitor just switch on? It may take some time for monitor to warm up.