When the car starts, it's quite noisy, but the noise stops after a while. Can anyone check what might be the reason for this? Is it normal?

When the battery charge is low (three bars or less), the engine starts to charge the battery. Once it reaches a sufficient level, the engine stops, and the battery continues to power the vehicle. That's why this situation occurs.

Try using Mobil 1 oil; its higher viscosity can protect the engine, but it might increase fuel consumption by about 1%. Just a personal suggestion. I used to drive a Japanese car and always used the specific oil, but the noise was quite loud until I switched to Mobil 1, and the noise noticeably reduced. You might want to try it once, and if it doesn't help, you can switch back to your usual oil during the next maintenance.

I'm the same way [I want to be alone for a while].

The sound isn't very loud, is it the starter?