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Rattling Noise

This just started today while driving home from work, not quite sure how to describe the sound, kinda like a mini jack hammer or rocks in a tumbler (attached video with sound). The weird part is: My car runs well aside from the sound, and the sound goes away when actually driving, only occurs when in park, or stopped. (under hood) (under car)

Opened the hood and jacked up the car to try and find the cause of the noise, sounded like it was coming from the engine, or just underneath (there is a box on the underside, not quite sure what it is, but the sound seems to be louder near there).

On a side note, checked my oil, it’s not low. And tried playing around with the pipe leading to the exhaust to see if it was lose - nothing.

Was involved in a hit and run just over 2 weeks ago (front left headlight was smashed, and fender was dented). I’m not sure if that has anything to do with whats happening now, but might help.

Thank you all for any replies!

This sounds like a exhaust hanger that has broken or rusted through.

Could also be a heat shield that is loose, but that would be a little tinnier sound.

Allow the exhaust to cool and try the following.
Jack it up and secure it on jack stands…please be safe…then grab the exhaust in a few different spots and give it a good shake. Shaking it, you may reproduce the sound so that you can pinpoint where it is coming from.


I believe that Yosemite is correct about this being an exhaust-related problem.
If the OP is not mechanically-inclined, I would suggest taking the car to a mechanic’s shop, and put on a lift, rather than trying to deal with it himself.

And, because it is possible that the recent collision resulted in a crack in the exhaust system, I would suggest having the exhaust system inspected a.s.a.p.
Carbon Monoxide is odorless, and if there is an exhaust leak, delaying a repair could have very bad consequences.

Sounds like an exhaust problem to me as well. Get it checked out.

Thank you all for the advice~ Will take a look at it this weekend

Man, that sounds awful. Maybe a broken harmonic balancer at the front of the crankshaft.

That’s not an exhaust rattle.

Sounds more like a rod bearing.


Another guess, a mini-jack-hammer sound can occur if the timing gets too far advanced for some reason. I had that happen w/my Ford truck one time when I accidentally switched two vacuum hoses finshing up a repair, which caused full intake manifold vacuum to be applied to the distributor vacuum advance at all times. The distributor vacuum advance is only supposed to get a vacuum signal during rapid acceleration, not at idle. tat tat tat sound immediately developed, but only noticeable at idle. That amount of ignition timing advance I guess is normal at higher rpms so it doesn’t make a sound then.

To me this sounds more like out-of-whack timing than an exhaust rattle… but the fact that it only happens when stopped points to the exhaust.

If it’s an automatic and stops when put in neutral, that would be another suggestion of an exhaust rattle. In “D” with your foot on the brake, the engine is under some load.


Engine (V-6, 4cyl, Super charged)?


I see from the picture (finally opened up) it’s a 3.5L V-6

Exhaust leaks become loader when accelerating, this is something crankshaft related. A loose harmonic balancer or a broken torque converter flex plate. If it is an internal engine problem like a rod knock it won’t be quiet when accelerating. Is the noise from the front or rear of the engine?

Pontiac G6 GT, 3.5L V-6, 2005, automatic transmission.

Lifted the car to check for loose exhaust hangers, cracks, lose heat shield and what not, couldn’t see anything, so took it into a muffler shop, definitely not the exhaust system. Was advised it may be a piston slap (which sounds reasonable, but to my knowledge the sound should go away once the engine warms up, in my case it doesn’t, only when actually driving), or a valve problem (don’t have much experience here).

Will have a look at the timing belt tomorrow.

On a side note, the noise occurs when in park, neutral, and drive, but disappears once the rpms go over roughly 1.2k (idles at 600-700).

"Will have a look at the timing belt tomorrow."

Okay, but FYI, the LX9 engine option, that 3.5L in this car has a timing chain, not a timing belt.

When I said “exhaust noise” I meant a rattle. Like a loose heat shield.
I’d still start there.

Take a look at these TSBs (Technical Service Bulletins) written for GM technicians.
@Nevada_545 was questioning this possibility, too. “A loose harmonic balancer or a broken torque converter flex plate.”


I’ve never heard a bearing knock or piston slap sound like that. It’s to irregular and tinny. To me it sounds like something is loose and banging around.

I’m also wondering about torque converter bolts . I know someone that started parting out a vehicle because he thought a rod was knocking & when he removed the transmission he found loose TC bolts .

Finally decided to take it into a mechanic, turns out something was rattling around inside the first catalytic converter (the one in the engine bay just below the manifold). When the engine would rev between 600-1200, it would create the perfect vibration to make the noise, anything higher and it would stop. Got it switched out, and no more noise.

Thank you all for the suggestions and help!

On a side note, I had taken it into midas previously in the week. Turns out the pro’s weren’t very knowledgeable.