Indeed.
The 1st graph axis is labelled "drehfrequenz", which translates as "rotary frequency". (Hz)
The 2nd picture, which is supposed to be a zoomed in version of the first has a vertical axis in unit "watt".
So I think the poster needs to explain exactly what's going on before he gets a meaningful answer.
The zoomed graph is showing a power fluctuation not a frequency fluctuation.