The hydraulic lifters can and do crap out, and they are pretty cheap.Did you notice if the noise was there both on and off throttle, as in coasting in gear?I'm inclined to think it's a non-critical failure if it went 2K miles of interstate drivingand didn't blow or get worse.
...BTW your Bieber avatar is awesome.-Malone
If those are rod bearings that is how they wear. Mains are opposite. They don't look good to me.
Is it possible that a precup can drop just a little bit and be kissing the piston? I am inclined to think it would have changed in tone or sound level after all those miles at high rpm.