A friend of mine has a 2003 I35 with 67K miles on it. It is making a noise that I am almost sure would be the timing chain / chain tensioner. Fortunately it is still under warranty, but has anyone else run into an issue like this?

Completely normal and every 3.5 eventually gets it. Repair would involve tearing apart the entire engine, if it's worth it to you to get rid of some noise then by all means

Otherwise just make sure your oil level is good as the noise causes no damage.

if I would want a motor that makes noise, I would get a GM 60* v6. motors should be quiet.

Just be glad we don't have to deal with intake manifold gaskets failing left and right.

haven't had that issue yet on either 3x00 we have.

Consider yourself lucky. Biggest performance boost my 3100 ever got was that repair.

neither 3x00 needs it thankfully. at least not yet...

If it's the guide problem (chain eats through plastic guide) eventually it will FSU, stuff will break, the motor will make horrendous noises, and more stuff will break while the engine junkifies itself valve interference style.

If it's a smoked exhaust valve bucket/shim (commonly refered to as a "lifter" even though it is technically not) on the rear bank, it's quite possible the motor is junk allready due to an oil consumption problem, it got so low & starved a few on the #1/rear bank, commonly caused by a bad rear-precat getting sucked back into the motor and wiping out the rings- which can usually be heard as a rattle around 1200 rpm's. The symptoms of the bad shim or "lifter" will be a constant metallic ticking sound heard at idle and while coasting, the sound is usually more pronounced on a cold motor. The timing chain/guide issue will sound like timing chain rattle (yes, I know, but it is it's own uniqe sound). The best way for most to differentiate or confirm either one is with an automotive stethescope, they are cheap.

I have an 02 I35, and im getting this rattling noise at low speeds/rpm's. When im cruising above 40-50 or just idling in park, i dont get the noise. i've tried revving the car while in park to see if i can mimick the noise, but nothing. Sounds like a lose exhaust clamp or heat shield, but took it to a mechanic, and he told me that nothing is loose under the car.

Wouldn't a timing chain make noise while the car is on and idling?

I agreee with everyone who said fix it...

I had my ac compressor f'ed up. It wasnt so serious when i bought the car it made a slight noise but went away from ac or heat was on. 2 months later it was so loud i had to shut off the car to hear wat someone was saying. Got it fixed.. 450 burned out of my pocket but it had to be done.

God forbid the chain blows and messes other things up i say fix anything.. there shouldnt be any problems with a car.