I would expect this from a Chevy but not my Ford.

I recently replaced the oe serpentine with a Gatorback and when I started my truck back up it was whining like Kobe after a Lakers loss...

It was very high pitched and it only does it when the a/c is turned off. If I turn it on, it goes away. My truck is only 9 months old, could it be possible that the a/c is going out?

 

Sounds like the compressor to me. Since your truck is under warranty seeing how it is only 3 months old I would take it into Ford and have them take care of it.

Richard

 

Did it make the noise before the belt change. If not, any poss. that it is not installed quite right. I know that sounds bad but it is actually easy to route it so that it works ok but is not going around the pulley s right........ Just food for thought

 

yeah, I noticed a slightly strang noise before I changed the belt. Also, I routed the belt like the diagram under the hood.

 

Might be worth your time to remove the belt agian and turn all of the pulleys by hand one at a time. You might find one that is not right and be able to lube/ replace it. Idlers can make noises that come and go depanding on the load put on the belt.