the title says it. on my way home from work i noticed the noise coming from my engine bay when it goes above 2.5k rpm, it doesnt matter if its under load or moving its just on the engine speed. i was mudding earlier today and i think it might have something to do with it, but why would it only happen at higher rpms? why not all the time? well its kinda late so i didnt have much of any time to look at it tonight but i will take a closer look in the morning. i am just wondering what are some of the possibility things i should look for that could cause this? any input would be appreciated

 

i had some thing like that only happened at 2000 rpm it was loose nuts where the header connects to the exhaust pipe

 

I would say something is loose and rattling at a certain frequency that you hit when the motor revs to 2500. Just check for anything that is loose. You could get someone to rev it to 2500 and you look all around on the truck to see where the noise is coming from and pinpoint it.