My Kett has an irritating noise when pedalling uphill. It appears to be coming from the seat backrest, probably some slight movement reacting to the hips rotating very slightly. Not sure if it's the straps or the seat tubes that fit into the sockets on the frame. Any feedback welcome!
How old is your Kettwiesel? Do you ride a lot in dusty or wet conditions?
I would take the seat cover and the seat tubes off and clean the tubes and the sockets in the frame. Also check for any damages like a crack in the sockets or similar. Then put it back on and hope the noise is gone.Kettwiesel AL mit Rohloff und Differential
IIRC I once traced back squeaking to the lower pivot of the seat back, towards the rear.
I can not remember how I fixed it, but usually I would disassemble, then clean it and if it still squeaked try some WD40.