I manage a new apartment complex and have a resident that has a vibration in an interior wall in the half bath. The vibration starts at 4 in the afternoon and gets louder and is intermittent. He hears it whether the A/C condensors are on or off. He has lived here a year and it just started.
There are 12 units in his building, and he located above the electrical panel. I have the builder, electricians, a/c folks and 2 maintenance men trying to find solve the problem. It is in a wall where there are no pipes, electrical lines. On contractor felt that it was coming from the electrical panel and nothing could be done. The resident is upset that I can't solve the problem.
Any suggestions? It is not coming from a/c, water pipes or electrical unless it is from the panel below his unit... no attics, no vents on the roor, tankless water heaters in the gargage.. HELP please.

