Sigma APO 70-200mm F2.8 EX DG OS HSM AF problem

I am at a loss, hope someone has an idea. Recently my Sigma APO 70-200mm F2.8 EX DG OS HSM has started "hunting" for focus in low light. I can hear the focus mechanism slamming back and forth rapidly. The lighting conditions are identical to previous times I have used it. I have a 7D, but the lens has the same problem on my buddies 60D In daylight it has no problems. I have a lighthouse trip coming up in 2 weeks so don't have time to send it in at the moment. Any ideas are appreciated.

hunting in low light is pretty normal. it happens to every lens. my 135L also hunts, or can't even focus when it's very dark, but that's normal to me. actually my siggy 50 can focus under the situation where the 135L can't, i guess it has something to do with the max aperture.

The lighting conditions could not possibly have been identical unless you're using a very controlled studio.

What seems like identical light to your eyes may not be identical light to your camera, as your eyes are MUCH better at letting in light than your camera is.

Also, all lenses will start to hunt in low light, using a flash with a focus assist can help with this, or turning on more lights.

Turn on all your focus points and don't use AI serve mode use single shot

It is a night and day difference like something broke inside the lens. One day it focused fine and the next day it just wouldn't focus. And by low light I am talking my front room with daylight coming in the windows, so really its not all that low. All my other lenses focus fine in the same light. Something changed. The lens originally focused fine even during nautical twilight.

I am using single shot focus.

Also using flash with focus assist helps a little, still takes 3 or 4 pre-flashes to get a focus lock.

Just irritated as hell with it because It didn't get banged or dropped. Just pulled it out of it's case and and it was like WTF is going on.

Thanks for the input.

7D/60D - mount the lens, put in video mode, and record what it's doing

(My 1st Sig85 lens was doing something similar: http://www.youtube.com​/watch?v=k6ge65WzVDo)