My 2001 f250 with V8 and 5 sp has a noise that always shows up exactly 2050 rpm and quits after 2400 rpm. This sounds like it could be a vibration or exhaust leak, but is more like a chatter. It is not pinging. I have 38000 miles on it. It is more noticeable on heavy loads and is not apparent on coasting. All exhaust clamps and manifolds seem ok. Performance is fine. I have heard this engine has forged pistons and wonder if they could make this noise.

I had the same noise and took it into my Ford shop three times before they finally found it. There is a small access plate on the pass. side of the transmission towards the engine. It will rattle against the trans. Give it a little tweak and all is good.

Try shaking your exhaust and seeing if a heat shield is rattling, visually inspect the welds as well. Those gas engine heat shields break all the time.