First annual after buying it. The pre-buy mechanic claimed he had checked the carrythrough for corrosion, but admitted it was a quick flashlight check and would not have found the problem, was which away from the inspection hole. Mouse nest in the insulation up there, probably happened when the plane was down for several months (at the seller's field) getting a new engine. Unlikely that it happened during my first year of ownership as there never was any evidence of mice habitation in the hangar I was renting.
I'm currently temporarily medically grounded and had the area above the headliner checked for evidence of mice recently as I know there are mice in the community hangar I'm in now, and the plane hasn't flown in nearly a year. Keeping fingers crossed that they stay away until I can get my medical back.