Hello MR Forums, I am currently experiencing a issue with my late 2009 27" iMac. Lately in the past few weeks my iMac has begun making not to say a loud noise but completely new audible fan whirring noise. My iMac has never ever made so much as a peep while running throughout the three years usage and having a quite audible fan noise is the first. Common sense suggests just general life usage and dust buildup, right? I think this is the case but I just need to ask for closure. The noise is pretty constant and consistant once it begins (say about 3 hours in whilst in use), no sudden stops or pops. The noise increases whilst I am streaming videos and playing games via Steam or web. What is odd is this activity is nothing new, I'm always watching videos and playing games and the iMac never had to increase its fan speed. Even when doing heavy resource activity such as having iTunes/Spotify open as well and working with the Adobe Suite. I did, upon research performed both a SMC and PRAM reset and the noise still occurs. I do have iStats Pro to monitor my system and I am using SMC Fan Control - I increased the settings to go to 1300rpm from the standard 1000rpm to see what would happens and it still occurs. So my question is, do I have a problem with my system or is this because of dust build up? >>>>>>TL;DR: 2009 iMac has started to make loud fan noises, performed SMC & PRAM reset - still occurs, is it a technical problem with the system or just dust build on the fan itself?