In PEM injection analysis, sometimes overestimation is happen.
One cause is the frequency conversion due to mechanical resonance of something.
So, the structure of the spectrum for darm and othre channels might be a hints of the noise path.

I investigated the PEM channels and QPDs around REFL table by my eye.
As a results, only IMMT1 trans QPDs (pitch) have similar structure with DARM around 280Hz.
I could not find any similar channels around 360Hz nor 520 Hz.

Plots for 

• ACC on REFL table : 240-310Hz, 320-400Hz, 480-570Hz
• MIC in IMCREFL : 260-400Hz, 480-560Hz
• ACC on IMMT ground : 300-400Hz, 480-560Hz
• MCI pitch : 240-400Hz,
• MCO pitch : 250-400Hz
• IMMT1 QPDA1 pitch : 250-400Hz, 480-580Hz
• IMMT1 QPDA2 pitch , 230-330Hz, 250-400Hz
• PRM pitch : 230-380Hz
• PRM yaw : 300-400Hz
• PR3 pitch : 250-400Hz
• PR3 yaw : 230-400Hz