This is going to sound like a total pedantic thing.. I have a mid 2011 iMac that does pretty much everything i need, but it has two annoying issues. a) the shadowy/light dust buildup at top corners of the display that's difficult to fix (it's not behind the glass, must be between layers of the screen) b) Occasionally the iMac makes a quiet but annoying bip bip bip noise. Originally i thought it was the central back fan, but it doesn't speed up if i increase the fan speed. It seems to start and stop for no obvious reason. On a usually whisper quiet machine it's distracting. I think it might be the PSU, if that's even possible. .. To fix or even properly troubleshoot the iMac I guess I have to disassemble it through the screen.. Before I even think about that, has anyone had similar noises, or suggestions? I know if i take it somewhere for repairs it'll mysteriously not make the noise and they'll claim it's normal. It's definitely not normal - it only started doing it within the last month. It's probably not the HDD - I run my iMac from an external TB SSD drive. It could be the internal HDD doing something though? There is no OSX partition on the internal drive at all, just windows. Thanks in advance!