whistling sound when engine is cold

i own a 2005 mazda tribute v-6.when the temperature outside is -5 and colder and humid there is a whistling sound coming from underneath the hood.i hear this while the truck is warming up in the morning.the whistling lasts for about 2min.then it goes away.sometimes it does it also when i'm driving on the highway revving at 2000rpm.the dealer changed the fan belt,tensioner,egr valve and the pcm.the whistling is still there.in the summer it doesn't do it.anyone out there has this problem.need help please.it's annoying.