So I took spectra of this, saved some references, controlled down Stage2, brought it back up to the same state and the peak was gone.  However, after a short time the peak started growing.  Starting out at the Isolation boosts, I found that by disabling the boosts on the X & RY dofs, the peak reversed and started shrinking.  It went down but there may be more dofs where this is coming in or the disturbance may come & go or grow and shrink because now I see the peak going up and then dropping down.  The first plot shows the full peak  (refs) and the currents are with the boosts disabled.  The PEM MAG channel is also shown.

Fabrice suggests we likely have a broad area of marginal stability and this feature which doesn't look like the Main 60Hz harmonic according too Robert (looking at Mag channels) is just a symptom.  It could be a DC motor that has locked here and maybe restarting a few things and it may go away but we need to fix the marginal stability if we can confirm it.  We will run a TF when able to look at the MIMO loop and go from there.