halper86: https://forums.whirlpool.net.au/archive/2304393
It could be your Panasonic’s power supply. I have a suspicion as you mentioned a few times that the phone line began to crackle while you were talking at the same time the noise went up, then when you unplugged it the noise went down again. I have seen this in a few other forums online after a quick google.
Makes a good case for moving off a sunsetting service to one that isn't vulnerable to this sort of interference.