The egr or Exhaust Gas Recirculation is a small canister on the front of the engine by the intake filter box. Honestly after listening to the video I doubt it is that. Exspecially if you say it is loudest or most definitive by the Y pipe. That being the case, maybe it is the oil pump or something top end. Usually fresh oil would alter the pitch in some way.
This is strange, very strange.
With 30k on that motor I really surprise that it would be a noisy pump, bearing, or anything.
Got me stumped.