Putting this on here on behalf of my mother in law She bought herself a 2014 21.5" iMac from the Apple U.K. refurbished store, basic spec model I think but with the 1TB HDD etc... The screen was flickering from week one, spoke to Apple and it was run through the tests (PRAM reset etc) and then sent to one of their authorised fixers and a new screen fitted as they said that was the issue... iMac came home, screen still flickered. Contacted Apple again, took it to one of their Apple stores and they've replaced the HDD and cleaned it all out inside, as they said their tests confirmed this was failing... Had it back 3 days and the screens still flickering! It's an intermediate flicker, nothing major and no screen going back etc... but it happens and it shouldn't! Does anyone have experience of this or similar and any suggestions?! The mac is under warranty, so Apple will be contacted again and no doubt returned to them, again! This is the spec: iMac (21.5-inch, Late 2015), 1.6 GHz Intel Core i5, 8 GB 1867 MHz DDR3, Macintosh HD, Intel HD Graphics 6000 1536 MB, Mac OS Sierra Version 10.12.1. Thanks!