2012 Focus SEL noise while backing up

My car made a grinding noise on the passenger side front while backing up. The noise was similar worn brake pad. I tried several time to recreate, unsuccessful. After arriving home, I check the brakes, pads (plenty of life left) and rotor look great.

Also I examine the passenger side cv axle, both boots are intact (no noticeable opening). But I did notice grease wetness (light coating) on the axle shaft right next to the outer boot (near wheel).
There was a light coating in a similar section of the inner fender and suspension section. No noticeable grease on the outer boot.

It is a 2012 Focus SEL with 170,000 miles. Note, I checked driver side…no noticeable problem. Prior to this, I notice periodically while making a slow u-turn to the left…the turn was not smooth (slightly bumpiness from passenger side axle).

Is there a potential problem with the passenger side cv axle? Is there any other tests I can perform to isolate the problem? Can it be anything else? How difficult is to replace this axle on the Focus?

Any suggestions or comments are appreciated.

Note: Prior to backing up, car was drive on freeway for 35 miles @70 mph. Also, was backing straight back.

Problem was transmission.