Quote Originally Posted by Flatlander
Hmm, I've been wondering if the back wheel is out of true. Does a spoke whisper when that happens?

I have access to a wheel struing stand, so I might just take it down there tomorrow and tweak it anyway to see what happens...

That said, I switched out my tires and the whisper is still there. I've also wondered if it's the reflectors on the wheels. Is that a possibility?
I'm not aware that spokes can whisper. They can ping. If there is a spoke that you can wiggle by hand it would be worth truing the wheel, but I doubt that's it. Do make sure the reflectors in the wheels are tight, and tighten every other bolt on the bike. Can you swap wheels with someone as a test?