04 Taurus chirp: Tranny or CPS??

2004 Taurus, 108,500 miles, Vulcan, has a chirping noise under the hood. I am not sure if the tranny is slipping or it is the Cam Position Sensor that I have read others writing about.

Notice it while driving at highway speeds, not necessarily under load (going up hill or acceleration)... It sounds like a "chirp" and the tach shows the engine revs a bit (about 100 rpm max) which makes me wonder if it is the tranny. However, I have also read that the CPS can do wierd things too... any thoughts?? No error codes, no problems staying in gear or shifting.

Thanks!

What side of the engine is it coming from? Passenger or driver?

What side of the engine is it coming from? Passenger or driver?
Thanks for the reply... good question. I drive quite a few miles (as you can tell) but 99.9% solo... Hard to locate exactly where the sound is coming from. If I were to guess, it SEEMS to be the right side (from a driver's perspective).

Wondering could this be a bearing in a pulley going bad? It matches all the symptoms... Just an idea :)