I have some old speakers in the house that I wanted to test. So instead of messing with the real stereo unit from the 80s, I bought a $30 stereo from Amazon, and new speaker wire.
The speakers sound okay, but there’s a hum coming from them all the time. Even with the stereo volume knob turned all the way down. Is this normal for stereo systems and I just haven’t noticed?


There are already no input wires (it is using Bluetooth) so I guess it is not a ground loop.
Thank you for the education! I’m assuming that the inputs, if they are grounded, can lead to the ground loop?