We moved into our home a year ago that was built in the 70's. Whenever we turn certain ceiling fans or lights on or when the A/C engages, there is a fairly loud popping noise that comes from inside the wall. We know it's related to these switches because we can cause the noise to reoccur by turning these off and on. We did not notice it until a few months ago. What could be causing this and is it dangerous? Should I have an electrician come out?