Tracking down a buzz can be very tedious sometimes so first let me ask you some questions:
You wrote:
I tried to move/shift the metal pieces that holds the knots of the strings a little bit, but this does only work for a couple of minutes, then the buzzing starts again.
I can only say a big THANK YOU for taking your time and writing such a detailed and interesting answer. I will keep this for future (and for times when hopefully I will perhaps have my own pedal harp).
Unfortunately the buzz occurs whether the lever is up or down. Mostly the lower strings are producing the buzz, I don`t have the problem with the upper strings. I
Anja, When you wrote “metal pieces that holds the knots of the strings” and “metal strings in the lower octaves,” were you referring to metal washers that your carpenter acquaintance installed between the bottom knot of the bass strings
sorry for not explaining everything very clearly, it`s because English is not my mother tongue… . My harp has no washers, but the string anchors are in fact little metal pieces – I didn`t know you could also take a used gut string! Thanks for letting me know all this, now I can talk to the maker of the harp again! And I am also very interested in the book you recommended, I will try to get a copy over here and hope I`ll understand everything! Thanks a lot Anja