What pinion do you use ? I use novak pinions with my mbx6 spur. The right mesh is very tight indeed, and it's totally quiet. The mbx6 spur is different than the mbx5. I had some noise issue with mbx5 spur, but with the mbx6 one I am very happy.
Inferno VE MMv3 NEU-CC 1515/1Y 4S "Flying machine"