I haven’t been able to return the pedal yet (it was bought in a neighboring city where my father works) but I’ve troubleshooted it a bit more and noticed that if I don’t touch the strings (or the metal on the guitar-cable going in to the guitar, or the pickups etc.) and touch the pedal with my foot, the buzzing increases instead of decreases.

In other words, if I touch the strings and touch the pedal with my foot, the buzz dissapears almost completely. If I don’t touch the strings or the pedal, I get a slight buzzing, and when I don’t touch the strings but touch the pedal the buzzing increases even more, and I get a bit of electric crackling and other scary sounds aswell.
(this only happens if the pedal is turned on).

now, I guess the problem is still bad grounding in the pedal, but I figured i’d mention it anyway.
(note that I’ve tried it with two different guitars with the same outcome, I always get a bit of a silent buzz when not touching the strings, especially if I have high volume etc. but not in the same way as when I use the pedal).