Apparatus and process are provided for suppressing interference caused by ground loop currents associated with two A.C. power-line operated electrical/electronic equipment units, such as an audio source and an amplifier, where typically the ground loop includes a shielded signal cable interconnecting the two equipment units. A signal representing current sensed from a selected region of the ground loop is amplified and injected into a second region of the ground loop as a counteractive current having polarity opposite that of the original ground loop current, thus tending to nullify the interference. The amplification may be made adjustable for optimal suppression. Ground loop current may be sensed by a sensing transformer coupled to the loop or by a pair of sense lines, connected to selected nodes in the ground loop such as respective ground terminals of the two equipment units, and providing the sensed signal to differential amplifier inputs. A counteractive current, delivered by the amplifier output, is coupled to the ground loop inductively by means of a driving transformer having a closed ferro-magnetic core surrounding the selected portion of the ground loop, such as the grounding conductor of a line cord of one of the equipment units or the shielded signal cable interconnecting the two equipment units.