During close-out work on the ETMX chamber, and while waiting for particle counts to drop, I took power spectra up to 50 Hz for both ETMX (QUAD) and TMSX (TMTS) suspensions (n.b. suspensions were still locked).

I observed a higher noise floor, of almost an order of magnitude, for the ETMX L2 (PUM) UL sensor channel (see ETMX_Original.png below).

To help determine if the source of the excess noise resides in-chamber or with the electronics chain I swapped the ETMX L1 and L2 stage in-air field cables at the Satellite Box (H1:SUS_ETMX-17 and H1:SUS_ETMX-17) and re-took the power spectra (see ETMX_Swapped.png below). It can be seen that the excess noise now moves from the L2 stage to L1, thus indicating that the source of the excess noise is down-stream i.e. with the field-cables or in-chamber.

Ideally, the above test should be repeated at on the air side on the vacuum feed-through to eliminate the field cable. However, most likely, this is an in-chamber AOSEM cabling/connector issue.