Yesterday, while testing an improveed filter for BS optical lever control, I found that, after closing the loop, there was an increese of the noise level in the spectrum (as I already observed in entry 1642), the level stayed high also after I open the loop and reset the filter. It went back to normal after I switch on and off the coildriver, but it got high again if I close the loop ( no matter whcih filter I use)

Pic1:  blue curve open loop spectra before with normal noise level (YAW top/PIT bottom). Red curve closed loop spectra with increased noise.