I searched, and found one thread where someone was asking about common problems and someone mentioned a whistling noise from the heat/AC blower was likely indicative of a failing blower fan bearing. But I couldn't find any other info on how people have diagnosed this. If there's a thread on this I'm missing, I'd appreciate a link.

Here are my symptoms:
1) Whistling sound from passenger's footwell area
2) Independent of vehicle speed (occurs while stationary or moving)
3) Dependent on blower fan speed (quieter at lower fan speeds)
4) Occurs w/ AC compressor on or off (AC button illuminated or not)

Does this sound like the blower fan bearing? The cabin filter was replaced ~7k ago. I haven't pulled the filter yet, but any chance there's a leaf/debris in the filter causing this? Or is this definitely the fan bearing?

 

Hard to give much help without hearing it but, if it's a whistling sound, I would think you have debris or a leak somewhere in the ductwork.
Did this just start one day(like one fall day when you parked under a big oak tree...) or has it gotten progressively worse?

 

It just kind of started one day. So this weekend, I actually pulled the cabin filter out (thinking there might be a leaf/debris), and then checked it, and the whistling went away. Turns out the white sliding bracket thing that holds the filter in missed one of the tabs it's supposed to lock onto, so the filter wasn't seated as snugly as it should have been. All fixed now. Good call!