Noise in Calls on LG L40

I've just bought a LG L40 cellphone, and I notice at first that I hear some noise on calls. Like that moment when a phone is about to ring and it's close to some speakers, you hear an interference. Well, I hear that while I'm in the call, at very low volume, but appreciable, because I have my ear next to the speaker.

I must say there's no big interferences here, I'm at my house. This didn't happened in my other phones.

Is this phone wrong from factory or some Android problem?