We have been sitting with the ISS off and the IMC unlocked (MC2 misaligned), and we see that there are a lot of glitches and the reference cavity isn't staying locked.

The second screenshot shows that this glitch also shows up in the PMC mixer signal, and less obviously in the PMC high votlage and ISS channels. 

We are now sitting with the reference cavity unlocked to see if we see something like this in the PMC without the FSS on, as of 22:05:49 UTC.

Edited to add:  We sat with the PMC locked without seeing glitches for 30 minutes, then tried locking the FSS again.  The glitches did not return in 30 minutes, so we can't say from this test if the glitches are from the FSS or the PMC.