Welcome to riding on aluminum rims.

As a part of braking the rims will in fact be "eaten" up by the pads. Different pads work differently with different rim materials. Pretty specific eh? You will find that when riding in wet conditions the wear and corresponding "scrapping" sound gets worse. As others mentioned - try different pads, clean your pads and rim surface. If it continues and you don't like it ...well...then you're doing something wrong.

I love it when newer riders obsess over normal things and see them as something truly out there as some sort of huge flaw. It takes me back.