Motor "knocking" noises

This may be old news to some, but just in case...I've seen a lot of people reporting they get knocking noises from the motor as the printer runs. I had this and I noticed that, while most of the time it was fine I did see issues with prints (uneven layers, string/fluff).I replaced the motor assembly but the same problem started again. Turns out the gear FF use in this is, lets just say suboptimal.I replaced the original FF gear with a 40 tooth brass gear (11mm external 5mm internal size) and the problem has been resolved.