Jim,
Excellent comeback there. I gather this is a "one hand procedure" ( no laughing !! ) 8>0 ........ as those can openings are quite small, in most cases, say 6".
But, before any cutting, please go the route Jim has described.
DO NOT cut any drywall until ALL avenues have been exhausted.
It may entails reaching up there, one-handed, with duct tape, caulk, silicone adhesive, fire-rated insulation, a combo of listed materials, or whatever can meet the heat factor of the cans, ...... etc, to kill the rattle.
Always mind the heat of the cans over time and proceed with caution, as safety is the ultimate goal, less rattle, of course.
Thanks Jim,
BOK