Beverly, Andy, Josh, TJ

In the low noise (and 22W into IMC) locks of 10/13 we saw a handful of whistles around 4 UTC and 8-9 UTC. They are the classic old-style whistles we also see at LLO: they couple in prcl/srcl, but not iss. They show up strongest in REFL A RF9 Q (see attached, along with strain). These were picked up by hveto which found them at the same time in the SRM noisemon, which is seeing the srcl feedback, almost certainly (so that noisemon is working right). The whistles aren't very numerous, but we wanted to give a heads up as this suggests a change, since whistles were rare to non-existent at LHO in O2.

Here are some scans for your perusal. 

• 03:53:01 scan: https://ldas-jobs.ligo-wa.caltech.edu/~detchar/hveto/day/20181013/1223424018-1223452818/scans/1223437999.2/
• 04:13:25 scan: https://ldas-jobs.ligo-wa.caltech.edu/~detchar/hveto/day/20181013/1223424018-1223510418/scans/1223439222.55/
• 08:56:09 scan: https://ldas-jobs.ligo-wa.caltech.edu/~detchar/hveto/day/20181013/1223424018-1223510418/scans/1223456187.02/
• 08:25:22 scan: https://ldas-jobs.ligo-wa.caltech.edu/~detchar/hveto/day/20181013/1223424018-1223510418/scans/1223454340.04/