5mph is ABS sensor/speed sensor.

Go get codes pulled at subie dealer and see which one it is. If no codes are shown, then the sensors are still within tolerances. Take all 4 ABS sensors off and the tranny speed sensor and clean the contacts.

Will fix the 5mph instrment cluster reader.
As for the noise, it can be a few things, are you sure it only occurs at 66mph? Maybe you're only conscious of it because you got used to it at that speed, try to pay attention if it increases as speed increases or it just shows up at a sudden speed.