We have a 1977 Avion we are refurbishing to use as a 'summer place'
up in NYS.
Besides finding floor rot in various places in the supposedly non-rotting
treated OSB-like floor substrate and the usual mouse droppings
and a couple of mouse skulls, we also found a relatively humongous
wasp's nest in the stove hood exhaust fan. We had found lots of dead
wasps on the window sills, and our sister-in-law said she had heard a lot
of 'buzzing' going on inside the prior year, but could never locate the
source. [We bought it from our brother & his wife.]
So here's the source of all that 'buzzing':
[Click for larger image.]
The outside hint:

First look after taking off the grease filter:

Fan unit taken out:

A closer look:

An overall look at it:
Cheers,
Norm/mezmo
If you have a house - you have a hobby.