Squealing or siren-like sounds?

It is a double-roller chain with steel gears. Might be Cloyes, I don't recall. Looked perfect when I recently had it apart. There are no weird scuff marks in the timing cover or on the block, so it's not rubbing on anything. Like I said I took the whole front of the engine apart looking for this noise and found absolutely nothing. I do not see how a timing chain can scream bloody murder, randomly. You cannot pinpoint the source of this sound, it is coming from everywhere. I've heard bad hydraulic (industrial) pumps and they kind of sound like this noise.