Hi everyone,
I'm having a quick-oscillating noise (not really a metallic sound) in the front of my 2007 TL Type S when the rear hits bumps such as cracks in the road or manhole covers. It's most noticeable while traveling slowly. It's easiest to replicate the noise when coasting backwards down my driveway and hitting the crack in the asphalt with the rear tires first. When the rear tires hit, it seems like the vibration/noise comes from the front-center of the car.

The car has about 125k miles. I've replaced all the shock assemblies about 35k ago, and most recently changed all lower control arm bushings. I can't remember when this started but now I'm trying to hunt it down since the LCA bushings didn't fix it. I gave up and took it to the dealership and of course they "can't replicate it."

Any ideas? Thanks everyone!

 

motor mounts?

 

Loose catalytic converter heat shield. I found this noise when I taped a shitty Samsung phone underneath the car to record a video while I was driving the car. Don't tape it to parts that heat up. I don't have to tell you that, do I? Check all four points where the heat shield is attached.

 

Aha you may be onto something! The rear pre-cat heat shield vibrates at 1800rpm religiously. Are you talking about one of the pre-cats, or the 3rd cat?

Also, the noise I'm looking to diagnose is not metallic, I don't know how to describe it but it doesn't sound like a loose metal part. Do you think it could still be the culprit?

I have an old iPhone so maybe I'll try out your video trick. I'll try not to melt the phone :-).

 

Yes, the main catalytic converter heat shield. It covers the underside of the converter, poorly welded into four points around it. It's right underneath your car where your shifter console is. It could be some other heat shield inside engine bay but you'll want to check this one first.

 

Okay it's definitely not the cat heat shield. Surprisingly it's tight. The rear pre-cat heat shield is loose however the dealership clamped that one for me.

Still stumped about this. Motor mounts do sound like a possibility but according to the dealership they're fine. They have never been replaced, though.

Thanks for your help!

 

I would check motor mounts. My 06 did this at low speeds. Shop said they figured it was suspension but when I looked at the one by the power steering reservoir it was obviously damaged. That solved it for me.

 

I have a similar problem. When I go over bumps, I get an intermittent 'bouncing around' noise from underneath that sounds like a muffler / tailpipe or something plastic like a bottle. Been under the car several times and can't find anything loose. The heat shield is intact and not loose. Motor mounts have already been replaced. Paul, our star mechanic in NJ can't even figure it out.

Any suggestions?
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Since I wrote this, I drove the car on a 2,000 mile road trip and the noise did not get any better or worse. Other than the noise, the car drove wonderfully.

I think my noise might be the radiator flopping around up there?? By design it moves in those grommets but it seems a little excessive. I can move it easily by hand and if I really smack it, the metal fan on the passenger side rattles.

Thoughts?