Volume control scrapes and rattle speakers

I usually have at cheap devices do not have very high expectations, but in this case I have some error of the instrument point. It should be mentioned that I ordered two (one blue and one red) ELTA6770 and thus not describe an individual case but the same mistakes in both.

1. The volume potentiometer produces scraping noises when turning. Something usually happens when the device is a few years old and dust is adhering.

2. Both units have a clearly perceptible vibration or humming in the right speaker, which can probably close to a resonance in the housing even at low volumes.

These two points mean to me that the equipment can not be used, since even the normal listening to music is unbearable. It seems indeed to be a exception, but I'm not ready again to let me send two of these players, then perhaps to experience the same thing.