I attempted to improve the quality of lock on the output filter cavity using the piezo by simultaneously agressively notching 100dB at 3.5kHz - 5kHz using the digital filter box and also locking the cavity while bypassing the HV amplifier to the piezo. This can be done by scanning on the laser frequency but still engaging the slow lock. No visible improvements were made. The transfer functions showed a much more linear regime compared to those posted in 11449, but the UGF was still quite low (<1kHz). I can post the TFs if anyones curious but don't have them as of writing this.