Looking at the 84Hz noise we have observed that the strongest effect on the DC powers was on B4 and B1, see Figure 1. The shape of the noise @ 84Hz in B1 DC showed also sidebands which were present also in the RF signals thus the noise on B1_DC is due to the coupling of DARM (B1_DC) with PRCL and MICH, while in B4 the noise shows a single peak which does not change shape/amplitude so it can be most probably the source of the noise. Talking with Alessandro the only action on SPRB done on the last maintenance (when the noise appeared) was the switch on of the stepping motors of SPRB. The switch off of these motors removed the 84, 155, 163Hz and 183 Hz structures, Figure 2.