We recently purchased a 1900' home. At inspection, gradual replacement of the wiring (as we remodel) was recommended because although the electrical system is in an operable condition at this time, a number of the wiring circuits
have been installed for many years and the insulation of wiring that old may dry up. Recently, i've noticed a humming/buzzing noise from some of the light fixtures on the second floor when they are turned on. We've replace all the bulbs and the humming persists. Is this a sign that we need to get the wiring fixed sooner rather than later? What causes this sound?