Just bought a 2012 5.0 Lariat with 120,000 miles. Got what I hope was a good deal on it. It's got what I'd describe as a consistent chirp that at first I thought was a belt squeak, but as I listened, it's not there, or it's barely audible at idle and up to about 1500 RPMs, and it gets louder as the RPMs go up. It's cadence doesn't change with speed. Serpentine belt looks OK. What else could be causing that?

 

Pulley?

 

Take the belt off and see if it goes away.

I’d go listen to it with a stethoscope personally.

 

Worth checking with stethoscope as mentioned, it's quite possibly a leaking intake plenum and/or the seals on it. A few people here have had that happen.