Ok, that buzz is from the difference in potentials - you do have a ground current running thru, and both power supplies are trying to handle that "ripple".
So, line isolation is needed.
I too own a Dell that uses single port - so I know there are power currents that flow thru the tip, sleeve and shield points on the connector.
I cannot connect the Dell to anything else without Windows attempting to communicate via those currents the ports "sense" thru this jack. So - I have to remove any power supply that can generate a cross-feed problem - so the device it connects to - needs to be under BATTERY power for itself and it will use the Shield (bottom contact - or last contact) on the sleeve to shield and reference - this is where those currents show up.
So caps to isolate all - and a dropping resistor of about 600 ohms from Sleeve to Shield and 1.5K resistor from TIP to shield - on THE PC side (no not radio - radio remains isolated thru CAP isolation on all contact points)
This is part of the problems with laptops and multimedia-based entertainment systems. Their ability to incorporate a floating ground point using single port - multi function interfaces.
So more than likely it's shooting a low -power current out looking for something to return back to it to tell it what to do. But, as a stand alone - it appears to itself as a high impedance "loop" between the tip, sleeve and shield points to allow the audio in, out and MIC functions like you'd have with a typical stereo headphone media for smartphones (earbuds - built in MIC with Call back, and Audio playback control features) thru a push-button switch.
So, line isolation is needed.
I too own a Dell that uses single port - so I know there are power currents that flow thru the tip, sleeve and shield points on the connector.
I cannot connect the Dell to anything else without Windows attempting to communicate via those currents the ports "sense" thru this jack. So - I have to remove any power supply that can generate a cross-feed problem - so the device it connects to - needs to be under BATTERY power for itself and it will use the Shield (bottom contact - or last contact) on the sleeve to shield and reference - this is where those currents show up.
So caps to isolate all - and a dropping resistor of about 600 ohms from Sleeve to Shield and 1.5K resistor from TIP to shield - on THE PC side (no not radio - radio remains isolated thru CAP isolation on all contact points)
This is part of the problems with laptops and multimedia-based entertainment systems. Their ability to incorporate a floating ground point using single port - multi function interfaces.
So more than likely it's shooting a low -power current out looking for something to return back to it to tell it what to do. But, as a stand alone - it appears to itself as a high impedance "loop" between the tip, sleeve and shield points to allow the audio in, out and MIC functions like you'd have with a typical stereo headphone media for smartphones (earbuds - built in MIC with Call back, and Audio playback control features) thru a push-button switch.