One thing I do with EVERY gearbox on EVERY tool I buy before I even use it is, I take it apart and clean out all the Chineseum wannabe grease and replace all of it with real synthetic EP grease. Always. Cheap Chineseum grease looks like thick Soy sauce and stinks too. I don't wait for them to rattle, I do that right away. By the time they start rattling, the damage is already done. Even the one cheapo HF corded 4.5" grinder I have an have beat on forever, is quiet as a mouse and never gets hot either.
No point in waiting until the 'horse is out of the gate' to rectify what will become an issue, no matter what and that applies to even the cheapo throw away grinders.