Just a quick FYI and update on my 2013 C-Max Hydrid with 55k miles: for the last couple months I've had an annoyingly loud whirring / grinding noise in the front passenger side of the engine compartment (somewhere behind the front bumper) only when I initially turn the A/C on. Doesn't matter if engine is hot or cold, of if car is running on battery power or not, this whirring-almost-grinding noise can be heard any time I hit the A/C button to turn the A/C on.
If the interior fan is on there's no noise up front, but hit the A/C button and that A/C componentry up front starts making a noticeable racket from quite a few feet away for a couple to few minutes till it all sounds normal again a bit later. A/C operation is unaffected and works well. Turn the A/C off then later turn it back on and it starts the same noise again till it again quiets down a bit later.
Figure it's obviously something to do with the electric A/C system on these cars, but since it's buried and sounds lower in the engine bay (above the plastic cover under the car), I'll let the Ford dealer look at it while it's in the shop having the transmission grinding problem diagnosed and treated (see my entry in that "Mileage and Build date for eCVT that have failed" thread in the eCVT forum).