I will just leave the picture of spectrum that shows the injected acoustic sound effects due to the oplevs.
red line: POY error without oplev feedback nor acoustic noise
blue line: POY error without oplev feedback but with acoustic noise
brown line: POY error with oplev feedback but without acoustic noise
green line: POY error with oplev and acoustic noise
You can see there is noise only at green line around 70 - 100 Hz. And it does not look like the acoustic signal is injected directly to the arms but the acoustic sound couples to the original noise source.