The noise the IS makes is slightlydifferent with each IS lens. I have the 300 F4 IS and there's a faint clunk and buzz; the 24-105 F4 IS has a buzz; and the 70-200 F4 IS has a slightly louder buzz. The IS activates when ever you touch the shutter button and it stays on for several seconds. You can notice the IS work by looking through the view finder, touching the shutter button, and it does take the shake away from the image in the viewfinder. You should take some pictures with the IS activated and check the results. I'm sure everything will be fine. Once you get use to how it works, how it sounds, you won't ever notice it again.