A few days ago I reported in an alog that whistles were back. We really only started to notice them at the end of last week when they became really evident, see for example this plot from the summary pages and all those high frequency, low SNR glitches! I've been looking to see when they first started. I can find whistles after the ifo was recovered from Tuesday maintenance on the 11th December, but not before. I plotted the IMC VCO frequency range in the last lock on Tuesday 11th December and the first lock after recovery; the results can be seen in the first attached plot. Before the ifo was recovered, the IMC VCO frequency range spanned ~78.94 - 78.98 MHz, whereas afterward the range spans ~78.90 - 79.02 MHz. This new range has persisted for the last month. I reattach the likely troublesome frequencies which produce whistles when something beats with the IMC VCO. So it looks like when the IMC VCO range expanded, and covered  ~78.91 and ~78.99 MHz, we see whistles.