Name that interior noise

[79BIG10]

Okay I think I have an idea on what it is but I need to ask if anyone can pinpoint it exactly. When I'm driving down the road just after going say a few miles down the road (few being less than 10) I'll hear a squealing creaking inside the cab under and behind the dash. It's only for about 20-30 seconds but it's noisy as hell until it stops.

Now I'm thinking it's something to do with a vent inside the cab because it only happens at different times. When I'm driving at night it doesn't do it as soon. When I'm driving in the day when I first start off in a couple minutes it starts up. I think it has something to do with the temperature outside to activate the vent. Am I thinking right and if so where is it and how to "grease it"?