doesnt matter, the sparking will upset the electronics
i assume your using non gen brushes. What i find is they dont contact the armature properly. if you take one out and look at it you will see the brush only contacts at one side and we want it in the middle.you have to take this high spot off with emery. goes without saying dont take too much.
I automatically take a bit off the brushes before i fit them all the time. Once you see where the high spot is you can do it
Dave