yes, you will get gear rattle in any gearbox when you have a lightweight single mass flywheel. It is an inevitability. Multiplate clutches make their own weird noises. Manual transmissions always have and always will be just a little bit clunky in certain conditions. I was always curious to see if Redline shockproof oil would cushion the gears and reduce the noise. Ultimately its the same reason why it’s stupid to run a solid flex disk or “guibo” which the entire damn world spells incorrectly and I will never forgive them. Lets all agree to call it a flex disk and never say anything that rhymes with guido.
Engine power output is in pulses and the deceleration between pulses opens up the gear lash. This is less prominent with a heavier flywheel as there is less deceleration between pulses. It’s happening in every gearbox, just less noticable/audible. The dual mass flywheel eliminates this.
Embrace the fact that its manual. Dont expect perfection. Install a really good shifter, freshen up everything you can, and make the experience of rowing gears as magical as it can be.