2006 f250. There is another whistle sound besides the turbo whistle. This whistle is a little louder and high pitched and it comes and goes?!

Wastegate?

Thermostatically controlled fan?

Dirty air filter?

No & No. Have an Arraid filter on there that has been cleaned. The noise comes and goes. It may do it for awhile then go away. Other days it will do it more often.

It happens when I give it gas, let off the gas or just on cruise.