I don't think so, because it wasn't doing it before, and the firmware does filter out high-frequency noise on the ADC. It also happens when the extruder is heating up and is 100% on, there is no noise likely to be generated by the resistor, but it could be picked up from somewhere else I guess.
I might expect a small DC offset when the power drops when the heatbed turns on.
The failure mode is that the temperature abruptly changes for several seconds, then flips to another value. I suspect it is thermal stress in the thermistor which is changing the value. When the hotend reaches a stable temp, the temp reading also stabilises.
I will also take a look at the signal with the scope.
I might expect a small DC offset when the power drops when the heatbed turns on.
The failure mode is that the temperature abruptly changes for several seconds, then flips to another value. I suspect it is thermal stress in the thermistor which is changing the value. When the hotend reaches a stable temp, the temp reading also stabilises.
I will also take a look at the signal with the scope.