When I first got my 08 JKU a couple of months ago, it had a slight noise. I couldn't pinpoint it due to poor hearing.
It started getting louder and i knew it was a pulley type noise. So I removed the serpentine belt and checked all the pulleys and found the water pump had a slight noise, not like I was hearing with the Jeep running.
Made me think timing chain, with 214xxx miles on it.
So with the belt off I fired up the engine and wow...... normal engine running.
Went and bought a water pump, replaced it and its been quite ever since.