You could try turning off the converter/charger or inverter/charger to see if the interference stops. It also can be caused by fluorescent light fixtures and other things that put out electric radiation. Also, check that your TV is plugged in to an outlet that is directly connected to shore power, not through an inverter. You might also put a 12 v meter in the power plug on the dash and see if power fluctuations of charger going on and off match the blips.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI