2005 Escape problem - engine noise / power take-off?

Hi, I recently bought a 2005 Ford Escape XLT 4WD. When driving at or above 65mph, the engine makes an abnormal high-pitched sound. The Dealer and "Ford Engineer" claim that this could be a problem with the "power take-off" controller. They explained this as a unit to control power distribution to the rear transaxle, usually engaged when the car needs to switch to ~4WD. The Dealer is replacing the power take-off unit, to see if this will fix the problem. I'm wondering if this is the problem, could there now be damage to the 4WD or other parts of the car? I just bought this vehicle brand new 2 weeks ago, so I'm worried about it being a lemon, or turning into one if it's not repaired properly. thanks in advance for any advice, Mike