It's via bluetooth, and the source is Pandora. I even googled Pandora and pitch change, and found some forums with folks discussing bluetooth causing this to happen, which has never been my experience.
It occurred to me that slowing the playback (eg, causing the pitch to sag) could be a fantastic way of dealing with a connection that's too slow. It would be far better than stuttering, even though many of us would find the pitch change really annoying. The instructor and my wife simply can't hear it, or say "I thought that was just part of the song".
Anyway, has anyone ever heard of this happening? Do certain products do it? Were the Pandora forums wrong and this is actually a Pandora problem? Of all of the bluetooth problems I've had in my life, I've never experienced this before, so I tend to lean towards it being a data rate issue on the cell connection and Pandora slowing the music down.