Whistle glitches are being seen with an increasing frequency of occurrence starting from April 22.
The stretches of time when they were seen over the last week are as follows:
* April 22 (Monday): between 09:00-11:00 UTC; this coincided with an Earthquake.
* April 24 (Wednesday): between 01:45-02:30 UTC
* April 26 (Friday): between 13:00-16:30 UTC; this coincided with a period of high winds.
Today (April 30), they can be seen throughout the stretch of Lock between 02:00-15:00 UTC.
The whistles are accompanied by an increase in variance of the VCO frequency and a corresponding low-frequency (4-5 Hz.) glitching in the IMC-F motion. (plots attached from Wed. April 24).
While high winds and an Earthquake might have been the cause on a couple of instances listed above, whistles have also been seen when the wind and ground motion has not been high. It is not known what causes the increased VCO motion at other times.
I have noticed that the variance between ASC DHARD increases when that of VCO frequency increases, for example, on the following days,
* April 22 (Monday)
* April 24 (Wednesday)
* April 26 (Friday)
* April 29 (Monday).
Please let me know if someone has known this correlation.