The neighbors may have the problem but no pinholes yet. Water quality related pinhole leaks in copper tubing is a widespread problem in many areas of North America. Especially the NW, upper Midwest across to the east coast from FL to ME. If in doubt, check with the EPA or do a goggle search for pinholes + “copper tubing” typed exactly.
Have an electrician check the building’s ground electrode for a good ground and then the plumbing for proper bonding, especially the water heater.
Have your hot and cold water tested for pH, DO (dissolved oxygen) and CO2 content. Water treament dealers are much more likely to have experience with the causes of this type problem than plumbers that are unknowledgeable about water quality issues. If you have a hot water recirc system you should have the water tested for silica, TDS, chlorides and bacteria content also. Bacteria will be killed by turning the temp up to 140f for a couple hours/days.
Quality Water Associates