Figure 1, shows the comb, which is at exactly 10kHz (or less than 100mHz away from it), so it is likely to be some digital issue.
Figure 2, there is also a line at 229.22kHz which is a factor few high higher than the 10kHz and is dominating the RMS, so the 10kHz comb is not visible when looking at the data time series.
Too look more closely I have notched 8 of the high lines above 100kHz, and also reconstructed the signal using the amplitude and phase at all the multiples of 10kHz
Figure 3, shows the spectra of the two construction and the original data, the 10kHz comb follows roughly 1/f, which could be explained by a sawtooth signal
Figure 4, shows the time series, after notching the 10kHz wave is somewhat visible with a fast rise and slow decay, and in the pure comb signal the decay looks more like a sine-wave, the rise time is not exactly at the second, but 23us behind.
