You mention that you just had the tires rotated - presuming you mean you had a shop handle it, I wonder if they might have horrendously overtorqued the lug nuts? People have reported that as a cause of bearing failure... not that that helps you now, as you're probably stock replacing at least one of them. I'd check the torque on those wheels - I bet they're on there with extreme force.

Either way, it sounds like A Bad Thing(tm) and you should probably get it looked at asap. Perhaps others have other thoughts?