New Rattle Under Car - Speculation Please
 

2009 C2S 194K miles

I am the one that usually has some answers for clunks and rattles, but I am stumped.

Going over sharp shakes in the road like tree root bumps at neighborhood speeds, I get a rattle from underneath towards the rear. It is not a low frequency clunk nor a higher-pitched clinky rattle... but a mid-frequency rattle. I have had this for about one year and it is not getting worse.

I replaced ALL control arms in the rear, sway bar links, had to remove the swaybar clamps not them either, and not that long ago, shock mounts. None of these changes affected the sound or nature of the rattle. When I had an alignment done a month ago, I was with the tech who I asked to grab rubber hammer and start whacking away.... nothing. Not the cats, not the exhaust parts, not the suspension parts.... cripes... WTF?

One thing I did not check was the transmission mount but.... I don't think it would rattle like that no? More of a clunk no? Three techs and me stared at the underside of that car with one guy whacking away... all stumped. I did not remove the floor pan (you don';t have to remove it to replace control arms, just a few screws and some box wrenches will get you there).

Regarding chassis ears, my ultimate diagnostic tool, I would not know what to hook them up to.

Peace
Bruce in Philly (now Atlanta)

Brake pad rattle drove me bonkers - worth a check - a light brake application should eliminate the noise . . .

Good luck!

THIS! I replaced several suspension parts front and rear. I bought chassis ears and tried them in many locations all to no avail. I took it to a local mechanic and he figured it out in 15 minutes. I replaced the brake pad retention spring clips and problem solved.

I had pad knock from old pad springs a while back. Mostly while getting on and off of the brakes. If the noise is in the rear I would also look at the support braces that hold on to the plastic trim back there. These are the ones I’m talking about.

https://cimg2.ibsrv.net/gimg/rennlis...0b800b9ec.jpeg

I’ve spent countless hours trying to find a rattle in the right rear of my 07 4S. Swore it was somewhere in the interior. Then started looking in engine compartment , etc. Finally found it was a loose screw for the rear bumper, right in the wheel well. Felt like an idiot, check the simple stuff first! Good luck! My car is now rattle free and much more enjoyable!

https://cimg6.ibsrv.net/gimg/rennlis...fb98cd9af.jpeg

What about the spark plug heat shields.
they're kind of tucked away out of sight behind the side muflers.
they're dense enough to make a mid tone sound like a brake shield(clank vs clunk due to more rigid metal in brake shield).

I haven't pulled the wheels yet... too cold... going to wait a few days when it warms up a bit.

Peace
Bruce in Philly (now Atlanta)

It's supposed to hit 70F here in Charlotte on Thursday and Friday. That probably puts Hot'lanta in the 80s. :)

I have a clunk that changes octave range and happens over pavement clunks and speed bumps sometimes, I think it's the aluminum insulation around the rear bumper to protect it from the exhaust? When it warms up here .....the same.

I suppose you could take off the bumper and all the insulation. Probably a 20 minute job.

It was 10 degrees here last week and just got above freezing Saturday. My garage floor still feels like 10.......

It was 7 degrees earlier for us and will be 67 on Friday I think. Don’t recall too many 60 degree swings in January.

Our normal high is 56 I think, haven't seen that yet. Had a little snow and now 2" rain yesterday and the same is coming today. I'm not a winter fan!

This car looks amazing. Wheel fitment is spot on.

Update... maybe I found it? Both cats are rattling. What do you think? Video with sound below...

When I had the car up for alignment and the tech went whacking away.. on the car... we did not hear these sounds. They only make the sounds when you hit near the headers... as you move the rubber hammer aft, the sound stops. I then took a long screwdriver and started whacking up where the headers attach to the engine all was solid. Even the spark plug shield was fine.

I jacked up both sides of the car and then went a-wackin-away on just about anything I could see... I did not remove the pan, but whacked where the pan screws were fastened to those braces (thanx Ed) and all was solid. I did here a ton of gravel bouncing up there.

So, what do you think? The rattle I hear from the car sound differently from this... these cats sounds are more tinny/tinckely and the rattle I hear over tree root bumps is more jangly like something is really loose.

Peace
Bruce in Philly

https://photos.app.goo.gl/DNjoccDJzt8aZdX66