We traced a potential problem with the prebuncher yesterday. By powercycling it last night we were able to show that this 9.5 khz disappeared. Furthermore this morning, the control module for it was found to be possibly deficient leading to changes in current and phase with no setpoint changes. Last time it hiccuped this morning, around 6am, the beam was lost. After crew restored beam, they autosteered the injector using the "A" laser (rather than "C" laser which they did at previous occurence). This is what reduced your background.