I made measurements of ringdown constants of the of this mechanical mode to get a measurement of the Q factor.

The measurements were admittendly quite ratty, and often the PLL would lock to some oscillation that it itself creates, giving many occasions where the oscillation vanishes immidiately as the injectoin ends.
This is largely due to the mechancial mode not being significantly larger than the noisefloor, causing PLL to lock to garbage.

Of the times I was able to excite the mechanical mode itself, I measured Q-factors of through the locked PLL amplitude signal:

• Q = 1.807e+06 ± 66650 (1 standard deviation)
• Q = 1.638e+06 ± 51260 (1 standard deviation)
• Q = 1.731e+06 ± 68250 (1 standard deviation)

So the Q-factor is approximately 1.7 million.

At the time of measurement, the frequency difference between the optical mode and the mechanical mode was 14.55 Hz.
Given the optical linewidth is roughly 1 Hz, this is "far" enough away to neglect optomechanical coupling and trust this as a true estimate of mechanical Q.