Its old enough to know better! Several Reasons for a 'Whistling' noise, but most common is leaking door/windows seals! If coming from Engine Compartment: check out Fan Belt/Blade, if it increases with speed, it could be 'coming from the Braking System! Most noises of this nature, are minor, just a nuisance! Good Searching, I googled your problem because I knew nothing of Problems with the PT's! Dr. Gene~Landrum, Theorist and owner of Automobile Repair Shop!
If it's coming from the engine compartment, then it's more than likely your fan clutch. Easy way to determine if it is, is to have the hood up and start the vehicle and then shut it off, while looking at the coolant fan. If it free wheels after the engine has been shut off, then it's the fan's clutch.
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