[Rrrrrrr]

Strange rattle

Another new guy here... I've got an '07, had a strange rattle around 2200 rpm, turned out to be the early stages of timing chain failure. A tensioner was going out and causing the chain to rattle.

Been lurking a bit on here, and figured it was time to post!
Just picked up a 2002 Frontier crew cab 4x4, and it seems to be in good shape with 200k on it.
Though, I've got a strange rattle that's sort of difficult to duplicate... it only seems to occur at 2500rpm while under load when warm, a bit easier with the ac on, and more evident with more throttle... almost sounds like a heat shield... but everything looks tight down there... nothing loose or rattling. Kinda sounds like a soda can full of gravel being shaken up... any ideas?
Already did some of the freebie mods, like the air box with the help of the forum here, so it's definitely the place for help, lol
Thanks in advance!