I just had the whole sqeeky noise issue and it turned out to be the lower idler pulley sqeeking right before the bearing froze and snapped my serpentine belt. On the Jeep Grand Cherokee 4.0 6 cyl. engine there are two idler pulleys. One above and one below to the right of the altenator. Once the belt was off I checked all the pulleys to make sure they moved smoothly without noise. Since the upper idler pulley made some light noise I ended up just replacing both for about $22 ea. The new belt was $30. So, after a little work all is good!