Whistle from Engine Compartment During Acceleration Over 65 MPH

Purchased this vehicle brand new with 23 miles; 2.4 Four Cylinder Engine. Around 400 miles I noticed a high pitched whistle when traveling on the highway during acceleration; heard around 65 MPH and stays constant during acceleration, as well as gets louder around 80 MPH. The sound disappears when I release the gas pedal all together (on rare instances the sound holds for a brief moment when I release the accelerator, but this has only happened a couple times). It seems when the gas pedal is only slightly depressed the whistle is most audible, while if I accelerate hard the whistle disappears (not sure if that is because of engine noise or not). I also notice the sound is most audible when traveling down a hill (again, I am not sure if this is because the engine noise is reduced, or I am only slightly depressing the gas pedal). I have taken the car into the local Dodge dealership where purchased and they opened a case with Chrysler as they were not able to find the sound (they did hear it). Dealership replaced the serpentine belt (did not fix issue) and confirmed the sound was not made when the A/C pump went on. At this point Dodge is stating it is a "normal" sound. I have also tried replacing the air filter with a different aftermarket air filter which did not resolve the issue. It seems to be coming from the center to the left side of the vehicle (relation to sitting in driver seat). The battery (accessed by taking off the front left tire) and the air filter are on this side, as well as what I believe to be the transmission. The sound is not made while the vehicle is in neutral sitting in my driveway (not based off RPM's), but rather only when I hit that golden 65 MPH mark.

If I can offer any further background information I would be more than happy to.

Thank you in advance for your very much appreciated support,

Tim