Robert and I investigated noise sources contributing to the optical lever spectra for ETMY in this entry using recently installed PEM accelerometers. We were able to identify and remove three noise sources:

29.5 Hz
Annulus pump that was left on. The pump has since been turned off and will be removed from EY today.

90-91 Hz
Power supply for optical lever laser on the receiver pier. We moved this to the floor by the receiver pier and seismically isolated it from the floor using inflated clean room gloves.

56.5 Hz
Power supplies on floor near receiver pier. We placed these on a seismically isolated platform using springs.

The above changes removed the peaks in the optical lever spectra at 29.5 Hz and 90-91 Hz, and reduced the peak at 56.5 Hz by a factor of 2. We believe there are other sources contributing to the 56.5 Hz peak. Attached are the ETMY optical lever spectra before and after the above changes were made (including spectra for a recently installed PEM accelerometer mounted on the receiver pier), and pictures of the three noise sources.

The 29.5 Hz signal was also found in the OAT length error signal before the pump was shut down, as seen in an attached plot.

DTT template used is located here:
/ligo/home/robert.schofield/12sAug/OAToplev.xml