Just switched my new iMac and it has the dreaded dog whistle, not as pronounced as my previous 3 replacements which were last generation. I was hoping the new rev would have ironed the atrocious quality control. I still have yellow discoloration but I can't be bothered. My lady needs a computer and she doesn't want PC. I'll give it a few more days and if I can tolerate the whistle I'll hang on to this one. At least there is no dead pixels.