I know this thread is over a year old, but my 2015 C-Max just started to exhibit this behavior. I can hear the fan on the AC fluctuate. It's like the whine noise goes up and down. You can defiantly hear it in the air flow if that makes sense. I'm confident it's not having to do with the temperature control. I'll bring it up on the next service but based on past comments, they won't find anything.