06 Five Hundred makes whistling noise on freeway at 60+ mph. Doesn't make any other noise like this at any other mph. Sounds like a tea kettle whistle.

 

Noises we hear when the vehicle is moving should be investigated by attempting to determine where they are loudest.

Whistling noises could be from wind noise or possibly loose clamps on a turbocharged engine to list a few.

Need some better info as to where it appears strongest. You may need to have another person assist you with this while concentrating on where you are driving.

 

It sounds like it's coming from the engine bay closest to the drivers side.

 

If it is caused by a mechanical condition , we should be able to create it

Did anybody do anything with the air filter lately?
If you can determine engine RPM when the sound appears, that might help
If we can create the noise at that RPM when parked,we have some idea where to go.
If it is strictly speed related and cannot be altered other than reducing speed , it could be something on the vehicle blowing air over an opening, like blowing over the top of a soda bottle. Wind noises can be confirmed by altering speed and direction. Could you be describing what sounds like a whistle to you , has anyone else heard it and how did they describe it?