My truck has a whistle that occurs while towing my 7500# fifth wheel. It occurs when my fan cycles mostly from high to med speed. My dealer is going to replace my fan clutch. Anybody else come across this problem, would love some feedback, Thanx

 

is it a whistle or a squeal??

 

mine made a loud squealing noise one time when i was pullling a car and trailor on a steep grade. thats the only time ive heard it tho.

 

it whistles when the fan has cycled from high to med speed and whistles until fan speeds up or slows.

 

Have a look at your degas bottle and see if there's coolant stains all over it. I have had several radiator caps whistling when they're venting, and it sounds like a kettle.

If it's venting, you have other problems (Fan cutch, EGR cooler, head gaskets, etc, etc, etc... could be any number of things, not necessarily just the fan clutch).