How noisy is my line? Audio Prism Noise Sniffer

Google “powerline noise analyzer” or “powerline noise sniffer.”  The typical meter has a numerical readout in some units, such as parts per thousand, and they also have a mini speaker that plays a demodulated form of the noise so you can identify the source as radio interference or a motor or electric arcing, etc.  

There are at least a dozen models available.

I saw the meter reading and demodulated noise from the meter speaker on a dedicated line running from a very expensive dedicated subpanel.  There was still, somewhat high level of noise, that was substantially reduced by a powerline conditioner.  The system had no audible noise, as such, without conditioning, but the sound did improve with conditioning—particularly with respect to creating a soundstage that seemed to float in space.  The meter being used was an Isotek meter, which is not cheap (about $1,000), but, $100 meters seem to work the same way.