high pitch noise

in my ranger, i have an archos 20 gb mp3 player hooked up to my pioneer headunit threw an rca / ipbus converter. i also wired the mp3 player so it can charge threw the cigarette lighter while im using it. i just took a cigarette lighter plug and splice it into the cigarette lighter. i ran the wires for the rca between the seats and under the carpet in the center of the cab, then up behind the dash to the headunti. the power goes between the seats, over to the door sill and up under the dash to the cigarette lighter. the problem is when i use the cigarette lighter toi charge the mp3 player while im playing it threw the headunit, i hear a high pitched whine. if i unplug the charger, it goes away. i thiught it might be because the power was to close top the rca cable so i bought sheilded cable and rewired them so they are separated. they are only near each other as they go from the mp3 player to between the seats, about 2 feet.

why is it doing this, and how can i make it stop?

any help would be great. thanks