Hello Gavlar 2021
That's undoubtedly bearings inside the gearbox. Gear ratios are made up by combining 2 or more various pinions, for example gears 1 and 2 might use pinion combination A/B, with 1 also using C/D and 2 using E/F, for example. Often first gear provides the drive for reverse when engaged through a reverse idler, for example.
You'll be looking at the 'box coming out for that, I'm afraid. However, a *good* gearbox repairer should be able to identify and replace the bearings quite quickly and for a modest price, but you'll need to check the rest of the bearings whilst the 'box is out. My opinion (not a guarantee) is that the repair to the 'box should not be expensive- the more expensive bit will be paying someone to take the box out.
I can put you in touch with a good gearbox repair company, though they don't take them out the cars- just rebuild units sent to them... Most garages that claim to repair gearboxes in fact don't- they send them to places such as the workshop next to me, charge you a large markup in the process. If you know which workshops to go to and you take the gearbox straight in, the cost is much, much lower and you get to talk to a specialist rather than- with respect to most garages- basically a fitter.
Good luck.