I have had a go at probing the RCA outputs of my TV(a Panasonic TH-L42U20A) using a digital oscilloscope, and have encountered an unidentifiable source of noise. The scope probe is floating, neither probe or ground clip is connected to anything, however my scope shows a strange prominent 'ringing' waveform even though the input is floating.

The probe is about 30cm from the rear of the TV, and the waveform disappears when I bring the probe close to the floor, appearing again when I raise its height to about 15-20cm above the floor. Attaching the ground clip to ground attenuates the waveform slightly, but still has considerable ripple.

I suspect this might be some kind of EMI from an internal switching regulator, but it is unlike any switching noise I have seen before, and is considerably strong as well.

(10mV p/div, 10us timescale)