Also, while I was working on the PSL table, I heard noise that sounded like a bearing rolling around.  I suspected the HEPAs, since the one on the north east corner of the table has a problem when it's turned up high (we've known about this for a long time), however turning off the HEPAs didn't affect the noise.  The noise is strongest near the back of the PSL controller on the shelf above the table, and the PSL controller box is vibrating.  So, I suspect that the fan on the PSL controller box is about to give out.

EDIT:  To clarify, I mean the Innolight's controller.