Finally I flipped the Phono/Line switch and the speakers emitted a very loud and awful static noise

My sub was making a horrendous robotic noise, like a loud scraping rattling sound

Some people reported an audible hiss/popping noise when the speaker is idle, I have not noticed it, but maybe my hearing is bad.

When the unit is turned on and there is no sound source connected, I can clearly hear static noise (woo/sss sound) from the speakers within a couple feet of range

Some people reported an audible hiss/popping noise when the speaker is idle, I have not noticed it, but maybe my hearing is bad.

The second one has static noise at Bluetooth.

USB connector is damaged, after a month of purchase, the sound will appear noise, really exaggerated.

My sub was making a horrendous robotic noise, like a loud scraping rattling sound