There is an intermittent rattling sound coming from the HEPA in the NE corner of the PSL table (right above the PMC, all of our input optics).
Steve says it might be a bad bearing, but he'll check it out in the morning and get it fixed.
MC was having a hard time staying locked, with no discernable reason from the control room (i.e. no big seismic, no PMC PZT railing). The HEPA was on 100%, so I turned it down to 50% to hopefully reduce the rattling, if that was what was wrong.