I live in a manufactured house. I have two electrical panels--one outside on the electrical pole where the electrical meter is at and another one in a utility room in the house. The one on the pole is grounded and I have a 4 gauge ground wire running from the outside box to the one inside.
Recently, I installed an electric tankless water heater that draws 75 amps and I'm getting static on my AM house radio every time that I turn on the hot water. I've been told that the panel inside my house to which the heater is connected needs an 8 ft ground rod. The heater is grounded to the panel.