I actually think it comes from the alternator , had this same problem and it sounds like it comes from the alternator . don't think it necessarily means there is anything wrong for reason they get noisy as they older .
Make : DODGE Model : CARAVAN Year : 2003
Manufacturer : DAIMLERCHRYSLER CORPORATION
Service Bulletin Num : 2100403 Date of Bulletin: MAY 16, 2003
NHTSA Item Number: 10002401
Component: POWER TRAIN:AUTOMATIC TRANSMISSION
TRANSMISSION TRANSFER GEAR WHINE SOUND. *TT