Last week I finished wiring up the charging of my Walkman into the car. By effectively buying a female Cigar lighter socket and wiring that into a 12Volt Supply I found under the center console. Then plug a USB car charger into this socket. From here my Sony’s Cradle takes a 5Volt supply from an USB socket. Once I had done this the Walkman did charge but I started getting a Hum or wine through the stereo.
After doing some research I found this is related to a Ground Loop problem. So today I fitted a Boss Ground Loop Isolator, and re routed the ground for the charging unit to the same grounding point as the head unit. This has made a huge improvement to the Audio quality, I still get some interference when I turn the volume right up on the head unit and press pause on the Walkman. So I intend to replace the RCA cables with some shielded ones, and also install a Automotive Noise Suppressor on the incoming 12V line to the Charging unit. I’ll let you know how I get on.