We live in a 1912 row house that I believe has joist pockets that allow sound and mice to travel freely between me and my neighbors' houses. For instance, my neighbor hired pest control to deal with his mice last winter and one of the dying mice staggered into my living room, clearly in distress from the poison. Assuming my hunch is correct and the joist pockets are to blame, what's the best way to repair them so that mice AND sound are abated? I've already rejected spray foam since mice can chew through it and it lacks sufficient mass to block sound.
The right way to do that would be to use metal flashing, fabricated to go around the joists and abut the pockets. Fill the spaces with metal screen or coarse steel wool (to discourage rodent teeth), followed by the foam for sound deadening, then seal it up with the metal flashing, bent to go flush against the brick and nailed into the joists.