I've owned this Canon 24-105 for years but I'm wondering if it needs service. All of a sudden, I notice that when IS is ON, it kind of shakes (up, down, sideways) and then settles. I can see shifting if that is the correct term, within the viewfinder. It never did this in the past. Anyone know if this is a sign the lens needs to go to Canon for a tune up? TIA.