2005 Mercury Grand Marquis - Rattling Noise

I have a 2005 Mercury Grand Marquis. It has developed a metallic rattle sound that is loud at idle and while running at the same speed. It goes away when I accelerate. I checked the oil and it looks good. The noise started off quiet so I ignored it. Now it is quite noisy. The rattle sounds like a stone rolling around in a steel drum.

My GUESS should be a heat shield.

I suppose I could go underneath of the car and see whether that is the issue, correct?

Yes, you could and should if you want to find the problem.

You didn’t tell us the # of miles that are on the car. It could very well be a timing chain rattling. If it is, it won’t rattle long… it will go BANG and the engine will become a door-stop.

Have a pro check the car over.

1 Like

I dont need a door stop! 112,000 miles. I am going to check underneath tomorrow and will follow up.
Will a timing chain sound like a stone in a can? Is that an inexpensive fix if it is a timing chain issue? I just got the car!


I looked under the car and it sounds like it is coming from the part of the exhaust system that connects to the motor. Not in the rear of the vehicle but under like the passenger seat. Any thoughts?

Nothing loose under vehicle. I do not think the noise is coming from the engine area. Sounds like it is coming from what i described above

Maybe a broken flex plate. That is essentially the flywheel passing engine torque to the trsnsmission. As I said before; Have a pro check the car over.

Could be any number of things, but the most common source for a rattle like that – at least from the posts we get here – is the heat shield above the catalytic converter. Suggest to double check that first. A length of old garden hose can sometimes be used as a stethoscope to narrow down the location of noises.

Here is what it sounds like. Taken from passenger side front

Holy smokes!

Is the Check Engine light on?


No lights on. Like I said earlier, that sound all but goes away with acceleration. At idle or a steady speed it sounds like that.


I just let the son listen to the video.

When the engine is cold, take rubber mallet and bang the catalytic converter.

If it rattles, that’s where the noise is coming from.


1 Like

Thank you for your time. I will put it up on jacks tomorrow and give that a try and post results here.

Like tester said, check the cat converter(s). It sounds like the material inside it has broken loose and is rattling around. I think that car has 4 small catalytic converters, but I may be mistaken.

Drivers side cat

Drivers side cat

Now it wont let me post video links!

Try banging on the pre-cat.


1 Like