Whine only on morning startup.

Since it first started to get real cold over the winter, in the morning, when I start the truck up, it starts without any issues, fan roars for a second and then goes quiet, ... moments later a whining noise will slowly start to fade in and then get constant. The sound is kind of like rubbing your fingernail along the rough side of a plastic zip-tie in a quick motion, only it's constant.. I've a few times popped the hood and tried to identify where the sound is coming from, its near the front of the engine but its ridiculously hard to tell... it's quite noisy, its loud enough for my friends to say "dude, whats wrong with your truck?" ill just tell em, "it'll go away in a minute" and it always does after a few minutes.

On a warm morning, it won't do this at all.

Alternator maybe?... bah, I don't know.