Yes It could be. take your time and look around very closely. You might find metal shavings in the bottom of the oil pan. I did...
I would like to mention I have the exact sound coming from the firetruck. This morning, I dropped the oil pan. I had lateral movement on all rod end caps except one. I removed one just to look at the crankshaft bearings and crankshaft. It was scored very badly. I called oneof my mechanic buddies to take a look and he agrees with me, the motor has to come back out...
New pictures with oil pan dropped:
http://rides.webshots.com/photo/2388959750080243953GXqkUO