I have been unable to find a combination of phases and gains to reliably damp these modes. I took a very fine BW measurement of them and it looks like our bandpass filter for mode 18 is 2mHz off (BP centered around 1000.294Hz, actual 1000.296Hz), but I can't imagine this is large enough to stop any damping.
The only time I have been able to damp mode 18, it was only at a rate of around 0.1 /sec and it largely broadened the RMS values for mode 20. Actually it seems to show up in the DARM BLRMS and other 2nd order violins with a period of ~88sec.
I'm currently leaving the two modes without any gains, where everything is stagnant, while I find some other potential solution.
It seems that the gain setting for ETMY mode 20 with a gain of 1 was potentially ringing up these modes slowly over the last day (see 2nd attachment). This gain setting is not in the guardian, so the node didn't have catch it.
I took us out of observing for about 45 minutes because the violin grd wouldn't let me change some of the mode gains on ETMY. I tried to see if some of the other modes that were somewhat close could be stopping us from damping 18 & 20, but that didn't seem to matter. I then tried to change which dof we actuate on. No luck there either.
Out of Observing from 2110-2155 UTC
ETMY modes 18 and 20 are effected by ETMY mode 12 damping, which should be held at a max of something like gain = 2 (I think that's right, but should be checked by looking in lscparams, since I left notes about the nominal and max gain for mode 12.
If mode 12 gain is greater than what's called out in my notes, mode 12 gain is drving modes 18 and 20 to increase, and mode 12 gain should be reduced. It's also possible that what worked for ETMY mode 12 gain last week is not working this week, since we just started damping this mode, so it's possible mode 12 gain should max out at a number lower than what my notes say.
Bottom line, modes 18 and 20 ringing up could be that they rung up, or it could be that mode 12 has too much gain.
... also, I took a very prliminary look at damping ETMY modes 18 and 20, and tested the values as found in their filter banks with low gain values, and there was no clear setting for gains that damped either peak, and some settings that clearly caused an increase. lscparams values for these mode gains were set to 0, both nominal and max gain, and it might be worth checking what they're set to now.
I wasn't specific in my log, but I did try to see how mode 12 affected 18 & 20 since it is pretty close in frequency. 12 didn't seem to ring up 18 & 20 at all for me, and with the gain of 12 off I still was unable to get any damping out of 18 & 20 through their filter banks.
The gain for mode 12 yesterday was set to 8, and this seemed to working the best. Anything lower and I saw a slow increase in that mode.