My first pair of homebrew speakers, built in 1979 when I lived in rural Louisiana, were huge transmission line systems using B-stock KEF drivers. They were so large that I had to do the final assembly upstairs in my room because they wouldn't have made it around the bend in the staircase. I named the left-hand speaker "Ferdinand" after Ferdinand Porsche, and the right-hand speaker "Irving" after Irving M. Fried.
Anyway when the time came to move on to something else, I opened them up to salvage the wool and hardware. And that's when I found a stash of about two handfuls of dry corn kernels inside Ferdinand. Apparently Ferdinand had a little friend. And like Vhaung's experience, no mouse poop. A conscientious little friend.
Ironically one of Ferdinand Porsche's most ambitious projects was called the "Maus". You can Google it.
Ferdinand and Irving exited the room through the window, as neither could make it around the staircase, and the aforementioned final assembly was not easily reversible.
Years later when I built speakers for relatives who lived in the same house, I installed heavy-duty screens on the inside flare of the ports to keep the mice out.
Duke
builder of overpriced mouse houses