The grounding problem in a kit plane is the lack of a metal airframe for the negative connection. Each ground lead, therefore, needs to be brought to the negative side of the battery. The ground loop appears when two ground wires are connected together with an imperfect bond. It causes a slight amount of resistance at the joint which introduces a tiny, but significant, voltage to appear. This affects sensitive circuits with high amplification, such as audio systems, often causing hum.
Corrosion produces the same effect.
As oxides build up in the connection, resistance increases and voltages are generated that cause interference. The answer is a carefully planned ground system. Check your manufacturer's manual, for example, to see if there are any precautions about grounding. Some require that all mike grounds, for example, be connected to single point. When planning your electrical system, here are practices which have proved useful.