Now that HAM2 and HAM3 are both using the same ground instruments for sensor correction, I looked again at the coherence betwen their sensor correction channels, looking for some possible noise line at 0.6Hz.

I am using the input of the FIR filter bank:

H1:ISI-HAM2_SENSCOR_GND_STS_X_FIR_IN1_DQ

H1:ISI-HAM3_SENSCOR_GND_STS_X_FIR_IN1_DQ

The figure on the left shows the coherence between HAM2 and HAM3 channels.

The figure in the middle shows the transfer functions.

The figure on the right shows the ASDs of HAM3, and the incoherent part betwen HAM 2 and  HAM3 signals. It is well above the theoritical ADC noise, but I don't see any sharp feature at 0.6Hz.