I owned a 100-400 a couple of years back but ended up selling it to buy another lens. Anyway I've now bought another 100-400 and the first thing that struck me (apart from the credit card statement
) was how quiet the IS seemed? I seem to remeber the IS on my previous version being a fair bit noisier. I know Canon have bought out upgraded versions of their IS system, do they automatically fit the newer versions to all IS enabled lenses regardless of model?

