Scary noise

I started noticing this noise on Day 2 of GWNF IV and I thought maybe it was because I was in 4WD, but I'm still getting it and it has become more noticeable (or maybe I'm just listening for it more). It's a kind of grinding noise that seems to be coming from the area under the center console and I can feel a slight vibration under the floorpan in front of the accelerator pedal (no carpet). It only happens when I'm idling in neutral. Maybe the drive shaft? It sounds like a rotation friction type grinding noise. I know that's a strange description, but that's what I'm hearing.

Would the throw out bearing cause the noise when I'm in neutral? There's no noise when I'm in gear. I did have some deep water crossings, so I'll check the fluid first. Thanks for the help.