I just purchased a 1997 Town & Country AWD and I notice a high pitch whining noise that occurs when I get to 35 - 40 mph. It's not very loud but, you can definitely hear it with the windows down, at least until the wind noise blocks it out. You can't hear it at all with the windows up. I was told this was normal on the AWD models. Is this true or should I worry???

Is it coming from the rear or front? or side?