I examined the sidebands of the OMC ASC dither lines today.  The excess noise around these lines is disappointingly broad, roughly +/-2Hz.  There are sidebands around the dithers at +/-0.18, 0.45, 0.49, and 1.5Hz.

The attached figure compares the sidebands of the first dither line (middle plot) to the low-frequency DARM noise (top plot).  The bottom plot is the noise around the violin mode.