The nominal modulation frequency is 6270777 Hz, which when sampled at 500 kHz aliases to abs(f - fsamp * round(f / fsamp)) = 229223 Hz. We should study the fast samples of B4 before demodulation, to see which sideband is the real culprit.

One potential source for the 10 kHz comb might be the SSFS_Ctrl process, where some signals are up-sampled from 10 kHz to 500 kHz.