Question about PreSonus Eris E3.5

I have been using these (and also the E4.5) for two years without any problems. Connected via the balanced 6.3mm jacks. Important: In most cases the hum is not caused by the loudspeaker but by a so-called hum loop (ground loop). This means that the 50Hz of the power line become audible as hum through a ring connection via the ground of the various devices (amplifier, loudspeaker, etc.). In such cases, the ground must be interrupted at a certain point (e.g. with a ground isolating filter or adjustable on the unit itself). Information on this can easily be found on the Internet. A second important source of hum can be so-called interference. This is caused, for example, by unbalanced audio cables (e.g. chinch cables) running parallel to a power cable or in the immediate vicinity of transformers. Whenever possible, balanced audio connections (e.g. XLR cables) should be used, as the audio signal cannot be disturbed so easily.