I just returned back from Sigma in Long Island (love having them "local" ), and spoke with a gentleman named Abraham. Took out my camera and it seemed as if he knew exactly what I was going to say before I even mentioned it. Loose element. It was late in the day, so he said if I'd like them to mail it back to me since it would take about an hour to an hour and a half to fix. I said no, I'll wait.
40 minutes later, he returned with the lens, good as new! No shaking! OS on or off. Smooth zooming! Looked at the paperwork, it said "Replaced OS unit N/C". So I guess it is the OS unit. So as for those saying the shaking/noise is "normal", it definitely isn't. Video will come eventually, but it would be pretty silent and boring :-p Not sure if the repair will cost others but I had brought my Sigma lenses to them earlier in the year and paid for adjustments then, and it wasn't taken care of. But give them a call, see what they can do for you.
Sigma Corporation of America
Attn: Service Department
15 Fleetwood Court
Ronkonkoma, NY 11779
Tel: 631 227-2036
Toll Free Tel: 800 896-6858
Fax: 631 585-1895
E-mail:
info@sigmaphoto.com