Looking at a spectrogram with very high frequency resolution (0.001Hz) over the course of about an hour and a half you can see a slight drift of the 29.2Hz line in ENV_WE_CT_ACC_Z. There is an identical drift seen in DARM as well. This confirms two things the line seen in WE_ACCs&SEISs and DARM are from the same source, and the line is not a calibration line or caused by some resonant (because of the slight drift).