I have a pair of first gen Swan M200 speakers I've been using with my PC for I don't even know how many years. They've been fantastic. Then suddenly as soon as I power them on I hear a hum. The hum ...

Here Kolvir reports the hum persists even with no input wires connected, so ground loop is not indicated. While you can always <I> try </I> lifting a ground, and certainly gain clueful information if ...