I had the same sound in my engine. when I tore the engine down to freshen it up, I found out that the noise came from my timing belt tensioner pulley. it was on its way to locking up. some of the noise could have been due to my timing belt started rubbing on the oil pump and a faint ringing sound from the ring on the back side of the water pump pulley popping off. it was a complete mess in there. hopefully that's not the case for your engine.
