17-55mm frame jump - is IS going bad?

My 17-55 has started to have the frame move up and and down as it focuses with either my 7d or 40d. After that it seems to stay normal for the rest of the shooting session. With IS off it doesn't have the problem. I'm wondering if the IS is starting to go out - the lens is about 4 years old. If this is an IS problem, is this a relatively fast repair in the US, ie less than 2 weeks?
TIA