EMC and Electronic grounding

EMC and Electronic grounding
The electronic control systems in one power plant are digital base and separated "one point" grounding system is considered for it.
In that power plant, the separated hole of electronic grounding is located far from control room, therefore the used cables for suitable interconnection between equipments and earth pit shall be long enough.
The electronic system is safe against effects of corrosion and vibration also grounding system loop currents that usually observed in "multiple point" grounding systems and may cause inadvertent noises. However that control system has some EMC problems. Investigations show a 700 KHZ noise interference existence in system that has created this EMC problem in power plant control system.

How can you explain the reason of existence of inadvertent noises?