Accessory Belt Tensioner
Serpentine accessory belts have elasticity and snake around a tensioner and pulleys that contain bearings. They begin to squeak or seize when worn, causing the belt to stretch or break.
The accessory belt tensioner applies consistent tension on the belt and pulleys. However, the tensioner's spring can weaken, resulting in a squeak, a flickering charging light, and accessory belt flap. In addition, if adjustable and the tensioner applies too much pressure or is overadjusted, the accessory pully bearings will wear and begin to squeal.
Removing accessories like the alternator and power steering pump during engine removal can result in pulley misalignment resulting in excessive wear on the edge of the belt. For example, misalignment problems are common after power steering pump replacement. Also, check for loose mounting, causing the pulley to become misaligned with the rest of the accessory drive belt system.
If the noise goes away after removing the accessory belt and starting the engine, the problem is in the accessory belt system; if it's still there, the problem is internal, most likely the timing belt or chain. Again, check with the manufacturer for TSBs or any special procedures before proceeding.