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.
The bearing is chirping in the back of the 2W Innolight laser controller. It is loud enough to hear it. I placed 4 soft rubber feet under the controller to avoid shaking other things on self.
The HEPA filter bearing becomes noisy at 50V
Keep it at 20V for low noise
The aging of the laser came up when the noisy bearing showed. ~10% down in in 4 years. That is pretty good.