Alright here it goes. I don't ask for a lot of help normally, but I am out of options. I have an exhaust rattle (I assume) between 2,900 and 3200 rpms. I had 2.25 inch exhaust run from 4-1 header back...no cat or resonator. I have had two mufflers put on because two different muffler shops said it was a loose baffle. The exhaust pipe is single walled and all welds are good. I have removed every heat shield and there is nothing within two inches of the pipe. The rattle only occurs under load...will not do it by revving to 3 grand, it does it in every gear at 3 grand, and only for 300-350 rpms no matter the speed. There is nothing loose in the car or trunk, nothing loose on the engine or firewall, and nothing loose under the vehicle. It's been doing it for around a month now and I have to make a trip to Fla in five days (9 hours) at a constant 3-4 grand on the interstate. I want to figure it out, but I am fresh out of ideas and do not have access to a chassis-ear or any other listening device that can be used while driving. Sorry this was sooo long, but I am lost. Any Ideas?