Tenant noise - considering adding insulation in interior walls

[Todd Bailey]

We have a 3 unit property, and one tenant moved out recently. She mentioned that normal noise from other tenants (baby, talking, etc) kept her awake at night. Got me thinking that there is probably no insulation or other sound barrier between the units.  We talked about having insulation blown into the shared walls. Not sure what to do about the floor. 

What do others do?

thanks in advance.