Hi Harold,
If the hum only appears when using the PC Client, then it looks like a problem with his USB headset or something
in that chain. It is not at the radio site.
He can try (borrow) a different headset, or buy one for a few Dollars at a store. Yes, a Bluetooth headset should
work fine, if recognized by Windows as an audio device.
Note that he can also buy a cheap USB hub and connect more devices that way, including the headset.
There is no difference as far as the system is concerned if he uses DSL or cable. This is irrelevant.
73,
Mitch DJ0QN / K7DX