Second row heated seats use an electric heating element. Not the Peltier style heating/cooling fan driven units used on the first row.
I'd be curious if the noise can be isolated to the left or right seat? There are two heating pads per side - 1 @ seat bottom and 1 @ seat back.
If the noise originates from is just one side, I'd tilt that seat forward and see if you can identify the heating element cable and unplug it if possible. Should be a 2 wire connector. Basically process of elimination - left or right seat, then upper or lower element.
