Tclaffy

So this is an intermittent issue and I cant seem to find any other cases. While running at high speed on the interstate, when I am not accelerating, I hear an electrical motor engaging and surging. As soon as I accelerate, then surging stops. That last time this happened, I was 45 miles from home. I pulled off the interstate and the noise ceased. It didn't do it again until I exited at home. It has done this before on that same exit which is about 1/4 mile long and has a speed limit of 45. As I slow down, the motor stops. My awd was fixed by a new module but now my 4wd lo is not working. I'm wondering if this is an out of control actuator? Any other ideas or help appreciated.