2006 Chrysler Town and Country Engine Whine

After I drive my van for a period of 1-2 hours (highway travel) something in the engine compartment begins to whine - loudly. It gets louder as you press the gas and as you slow down it gets quieter but never goes away even when parked. After it sits for an hour or so - the whine is completely gone.

Someone told me that the serpentine belt will whine when it gets hot but I've had this type of belt on other cars and never had this problem.

If anyone has any idea what this might be I would appreciate the info as I cannot afford to have a mechanic play a quessing game at my expense.

Thanks bunches,
Deb