Edited from an earlier post...
Are you sure it's fair to say that it's lens that's 'hunting'? Perhaps, it's your camera body that's recalibrating.
When I mount the 55-300 on my K20D, I simply AF on a distant object using my planned focal length and let the camera and lens synchronize. Once that's done (it takes a couple of seconds), I've found it to focus as quickly and accurately as my other non-motorized lenses using about the same focal length. As to noise level, it's about the same as the others, too. I see all of this as part of 'getting ready to go' and no big deal.
Have you tried MF?
It takes some skill, but it's total stealth and you are 'spot on.'
--- my 2 cents...