Mystery exhaust rattle

I semi-recently put headers on my is300, they came with a fun exhaust rattle that was coming from several places like the muffler and resonator. After a little while I finally got around to replacing those. I have a flowmaster 50 series muffler and a Jones Exhaust resonator. The rattle has been greatly reduced, however I still have some rattle under acceleration only above 3k rpms all the way to redline. It’s quiet when I’m crusing, but comes right back if I give it much throttle and my rpms are above 3k. I’ve had the car up on the lift and I can’t see any visible marks where the exhaust might be hitting the frame or something else. I have no idea what’s rattling and it’s really starting to frustrate me. Anyone have any ideas, or magic ways to check components?

Rubber mallet, but only after the exhaust has cooled off.

It’s likely a loose heat shield somewhere.

I put the car up on stands and had a buddy rev the motor. Helped me figure out where my rattle was coming from.

1 Like

I second this. Probably a heat shield.

The exhaust has no heatshielding on it anymore, and I’ve checked the body side heatshielding and didn’t notice anything obviously loose, not that it means it’s not rattling, I just didn’t see it. I think I’m gonna try the ole rubber mallet and see what it says. Maybe the new muffler has a rattle in it. I’ll update y’all afterwards.

Most likely places: Heat shield over exhaust manifold or the one over the catalytic converter. The location of the sound should help decide which if they are not really close together.

The other one I had was where the tail pipe went over over the rear axle support assembly. Unless the car was going up and down just wiggling it when stationary aggressively wouldn’t hit - part of problem was the worn rubber support isolation piece between the frame and exhaust pipe.

has anyone suggested using zip ties to lock down the rattling part? better yet, just zip tie parts that aren’t even loose yet. don’t cut the stray excess ends. have a car covered in zip tie feathers. it will flutter as it travels like a massive beautiful zip tie bird

Ahh the old zip tie on the drive shaft trick is always fun.

I’ve been on the receiving end of rocks in the hubcaps. It back fired on the guy who put them in there.


Then the lovely hum of the fluttering zip ties will mask the rattle of the exhaust! its the perfect plan!


Hey man! What’s the rest of the story? Unless it involves something that isn’t past the statute of limitations.


Did some light hammering on the muffler last night, and wouldn’t you know it! there was a lovely tinny little rattle from the muffler when i hit it. I’m gonna put the car on the lift around lunch today if its open and work doesn’t chain me to my desk today to do it again and see if i can better pinpoint the source.

One order placed, and one shipment of parts later and it looks like I’m gonna try and build a new exhaust.