Strange engine noise while towing

[JRJ04]

how loud it is depends on how much it is engaged. sometimes mine will only kick on for a second and then kicks back out. when it does this, its not fully engaged and consequently isnt that loud.

 

[BigBlueF350]

Drove 55 mph today and did not hear the noise. Once I got to 60 I could hear it cycling again and there was a load on the motor each time. It was more frequent today and it was hotter this afternoon than last Saturday. I'm fairly convinced it's the fan clutch cycling. Thanks for everyone;s input!