It's not the voltage regulator/brush holder, it's the other solid small
rubber box thing that has a wire that goes into and attached to the diode
plate I think? Is it some kind of noise suppressor? Is it vital to the
alternator function? Asking cuz mine came loose, the wire came unsoldered
from the plate inside. I do notice some engine noise on my stereo now, very
little, before there was none.