Yes I searched the forums before posting this thread, but I could find anything that helped. Specs of my system: 2.8GHz iMac with 750 HDD and 8800 GS And now the problem, since the update to 1.5.3 (I think I didn't hear it before) I can hear a low tone humming coming from the area where the hard drive and most likely the power supply is (upper middle of the monitor). The noise is not very loud but the frequency is annoying and it is alternating in a 5 second rhythm (getting louder, disappearing, getting louder...). Because of the frequency I can even hear when watching TV or listening to Music.... It is most likely not the fans since they are running at normal speeds and turning them up to higher speeds does not change anything with the sound (still same level) It also is not the display humming described in several threads here (I tried changing the brightness and even tuning off the display) I also tried an SMC reset (turn off pull out all cables and wait 15 secs, I waited a minute just to be sure) It there anything else I could try? I can't send it in because I really need it?