Ford Fusion 2007 SE I4 - Grunting!

[Wheelman]

HELP! my 07 Fusion SE I4 is making an awful grunting noise on cold start when it's damp/humid out. I figured maybe it was in the ignition so I installed new spark plugs, no luck. The dealership told me it was the belt tensionner so I put in a new one, again, no luck. the noise happens when the engine is cold and it's humid outside and I put it in gear. when I turn the A/C off, the noise is less so I figured it was something belt driven but I can't find it. also, once the engine warms up, there is absolutely no noise, purrs like a kitten regardless of the weather or the belt driver accessories turned ON/OFF. my local mechanic is also out of ideas... the noise is a weird grunt that seems like the valve train is having an awful hard time and it's oftenly complimented with a belt squeaking noise. the serpentine belt and its idler are relatively new (20000km) and the car has 120000km on it. there is no distinctive loss of power when grunting though. I'm running out of options and those trial and error parts are starting to take their toll! Any ideas? Please Help!