Hi guys, I'm a newbie in this forum. My native language is Spanish, so apologies for my use of English.
I received my brand new imac 27' late 2012 last 22th January and after dealing with the humming sound due to the resonance effect with a cheap ikea desk, I decided to move it to another table, placed in a lighter room. At this moment, I noticed the weird clicking/popping noise in a random fashion that appeared to come from the bottom part of the screen and which seemed to move from left to right.
After many tests, I thinnk it is caused by the screen glass itself due to the warming of the display. This is the reason why I didn't realize before, when it was placed in a darker room. In that place, the dimmer was very low and the screen barely made those sounds, so they were almost not noticeable. But when in a lighter room, the "Orchestra" began.
I've arranged an Apple Support appointment and they are going to call me this afternoon. I was thinking on asking for a replacement but I'm not pretty sure about it because other people said their replacement units made exactly the same noise and don't want to assume the risk of receiving a unit making the same clicking noise and with an extra defect like dead pixels or so.
This morning I realized that if you gently press the black part of the glass in the near down left or right corners, you can reproduce the noise, even it stops for a while. As I said, I think it is caused by glass dilation cycles, and increases when the dimmer is set high or when the screen is in resting mode.
Anyway, it's quite annoying for a very expensive machine which should be perfect.
Cheers.