To clarify the mechanism of the generation of electromagnetic (EM) noise, current and radiation noise up to the GHz band generated by slowly breaking silver-compound contacts were investigated experimentally. The current and radiation noise at the GHz band were observed. It was demonstrated that the frequency spectrums of the current and radiation noise correspond to the frequency responses of the circuit admittance and radiation efficiency of the experimental setup, respectively. It was revealed that even if current noise at the GHz band is very small, it can cause a large EM radiation noise because of the high radiation efficiency. From the time-frequency domain characteristics of current noise, it was clarified that the peaks of current noise at 10 MHz band arise immediately after the initiation of the arc discharge and the transition from metallic phase to gaseous phase. On the other hand, the peak current noise above 100 MHz arises immediately after the initiation of the arc discharge.