sudden twang- a couple things
PA speakers are mounted below the overhead storage ( mostly ) so people standing in the cabin are less likely to hear PAs especially if there is noise in the cabin
1) the 74's I'm familiar with have the PA speakers mounted in the ceiling. Yours may be different, but I doubt it.
the fumes could well go into the pack inlets causing smoke /fumes in the cabin
2) The pack inlet air comes from engine bleed air- the NACA ducts that you see on the lower fuse are ram air inlets- that air cools the heat exchangers, and doesn't enter the cabin. Unlikely that smoke/fumes from a wheel bearing fire are going to enter the cabin that way.
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