Bad Exhaust Bypass or Bad Cat?

I have an issue that started recently (95 w/ 18k). I get a loud metaliic rattle sound between 2500-3000 RPM (sometimes lingers a bit up to 3500). It happens accelerating or decelerating, clutch in/out. Sometimes I think I can hear it faintly across the RPM range, but its like an instant noise maker switch 2500-3000 RPM.

I assumed it was the bypass valve. I wired the valve open and even disconnected the vacuum tube, still there. Is it my cats already?

TIA
-Aron

 

Update: 99.99% sure the rattle is forward of either the bypass valve or the cats. Funny part is you hear it almost in stereo like its coming from the top of the engine? While it might make me think valve train, I'm pretty sure I hear a lower volume of the same rattle when passing over bumps - like a loose part.

Is is possible for the headers or something like that to trap a lose screw/bolt that might have dropped on them?

 

Sounds like its mostly coming from the driver's side around the y-split either the back of the header, front of the cat or the couplers at the y-split.

I checked & tightened the heat shields under the y-pipe. Using a rubber coated hammer handle to tap various areas of the exhaust system from the headers to the tips generates a rattle in that junction zone as well. Nothing appears loose or moveable and everything looks visually healthy. No sound or indication of exhaust leaks. Applying some pressure the heat shields on the headers, y-pipes, or around the split couplers seem to dull the noise.

Short of any other ideas, I think I'm down to having to pull some components off to isolate it.