Identify this crunching noise : 300te 4matic
 

Driving home today I heard a rubbing noise followed by crunch/clunk that felt like it slowed my car down for a moment, then immediately went away. I pulled over in a parking lot and my friend who was walking beside the car noticed it (loudly) come from my right rear wheel.

When it's not making that noise it is very quiet.

I suspect that my outer cv joint has failed somehow, but I was able to drive the car home with no issues until I got on my street and the noise happened again. The car drives normally otherwise. Wouldn't a failed wheel bearing make noise all the time? I would imagine it would hum at the very least if it was the bearing.

Anybody ever experience this before?