my tintop Syncro (2.1 WBX) has the similar  whistling noise from the right
rear (or about). The sound is quite similar to a sound from a turbo -
beginning low whistle to a medium whistle (I wish I have a turbo ). I get
the wheel bearings checked... nope it's not it. My mechanic and myself
assumed that the whistling noise is from the alternator pulley (the one
with a small fan on it), or the friction from a belt.