The violin mode harmonics overlap with the ~15070Hz test mass bulk modes.  This may explain the mystery modes that have been rung up in the vicinity at Hanford alog27659 15063Hz and Livingston LLO alog20100 15085Hz.
This spectrum was taken from these measurements alog27743.  Two violin mode harmonics are visible between 15kHz to 15.1kHz and 15.5kHz and 15.6kHz.  Several test mass modes are also visible.  The violin modes were elevated and we were actuating on 15077Hz ITMX mode and 15072 ITMY mode (which are very large and far off the top of the plot).