Rattling or Metallic Noise at 3200 RPMs
 

I posted a while back about a transmission noise, but I was mistaken. The noise has nothing to do with the transmission.

Today I was able to recreate the noise in park at 3200 or higher RPMs. It's not all that troublesome or shocking, but something's definitely wrong. I'd say it's a squeaky high-pitched sucking, scraping or rattling sound of some sort.

The sound seems to come from the engine side of the firewall, somewhere in the vicinity of the glove box or lower.

Is something in the Exhaust Manifold wobbling? Catalytic converter? Any other ideas?

Baffles do come loose in mufflers and converters but the sound and occurrence may be different on every one. Can you get a long screwdriver and probe with the handle pressed against your ear? May not be doable in this situation but it works many times.
Good luck.

if you have a pre 2006 vortec; check the exhaust manifold studs. they break and at higher engine speeds the exhaust leak will whistle past the gasket.

That sounds like it could be your culprit to me