I'm not certain if anyone answered your question dealing with the grinding noise without opening the camera. Anyway, you need to open the side. There are a variety of gears and levers, and random lubrication can cause some of the small levers to stop movng freely. It is usually possible to quiet down YashicaMats by applying a light coating of grease to the winding mechanism gears. But this needs to be done carefully and thinking about where grease/oil could migrate over the years without causing problems. It isn't a simple process to open up the side and lube it; not difficult but not simple, if that makes sense.
I'm not familiar with the 124G specifically, but I can say that older YashicaMats were, well, a bit less than precise in construction. There are only a couple of adjustment points for basic operations. I think Yashica's basic philosphy was to assemble the camera, see if it worked, if it didn't throw it in the spare parts box and move on to the next one. Variation in fit of gears and such is to be expected.