I just finished unboxing my new-to-me Canon EF-S 17-55 f/2.8 IS and so far I love the size and weight of it.
The very first thing I noticed as soon as I mounted it and flicked on the IS switch, however, was a noticable whirring noise that I didn't hear on my 18-55mm IS or 55-250mm IS.
Is this normal? I'm guessing the IS assembly needs heftier components in order to move the larger lens elements but I wasn't expecting it to be so loud!
Here's a short video of what I'm talking about: http://vimeo.com/8627691
Audio comes from the onboard mic on my T1i so its fairly loud in the video, but my face is right there when I'm using the viewfinder so its pretty accurate.