I have a 02 f4i with a stock exahust,has about 16k miles, and when i get around 5k and up i get a constantgrinding-rattiling sound but when im in low rpms it sounds fine,but whats weird is if i cold start it and ride before it hits like 110degrees it doesnt make that sound but as soon as it heats up it starts grinding again....DOES ANYONE KNOW WHAT THIS IS??? is it my exahust or my trannie or what??? or am i just dumb and this is normal (i hope not)