Metallic rattling noise coming from exhaust pipe

May 28, 2013 7:33 AM

Recently my car (2008 Vauxhall Zafira) has started making a metallic rattling sound when (a) the engine is turning over at very low revs (i.e. when starting the engine) and (b) when going over bumps. When the engine is idling, or when driving along on a smooth road, the noise disappears. I can recreate the noise by grabbing hold of the exhaust pipe at the back of the car and wiggling it from side to side, so I assume that the noise is due to some bit of metal coming loose and banging around. I'm quite keen to fix this myself; can anybody suggest a more specific first troubleshooting step than "crawl underneath the car when it's cool and try to find the loose part"? I have no way of raising the car up, but I reckon if I park it with one side on the curb I can get underneath and take a look. If successful, I will update this thread with my findings :-)
posted by primer_dimer to Travel & Transportation (14 answers total)

I can recreate the noise by grabbing hold of the exhaust pipe at the back of the car and wiggling it from side to side...

Sounds like an exhaust hanger has broken and is allowing the piping to bounce and bang around.
Is there a local muffler shop in the area, where someone could put the car on a lift and take a look?
posted by Thorzdad at 7:37 AM on May 28, 2013

Best answer: It will be, in order of likelihood:

A loose or broken hanger.
A loose or broken heat shield.
A loose or broken joint.
A loose baffle in the silencer.
A suspension top link come adrift.

Take it in to a grown up to have a look. Do not let them con you into anything ridiculous like a new exhaust system.
posted by BenPens at 7:53 AM on May 28, 2013

Best answer: If it is a higher pitched rattle (like the kind of sound an empty tin can might make) then it is likely a heat shield either on the exhaust or on the car that has come loose.

It could be connected to the exhaust or the body. If on the exhaust it will either need welding back on or the exhaust section it is connected to will need replacing. If it is mounted to the car it may need a new clip or re-bolting back to the body.

If it is a lower frequency noise (a bumping kind of noise - possibly even felt in the car) then the exhaust itself has become misaligned and either a hanger rubber has failed or the hanger itself has failed on the exhaust.

It also could be internal to the exhaust, although I think this is less likely.

Easiest way is to jack it up as best you can and wiggle the stuff on and around the exhaust, or have someone replicate the noise while you are under there to pinpoint the noise by crawling around and listening. The fact that you can replicate the noise without the car running is the perfect helper to finding this.
posted by Brockles at 7:55 AM on May 28, 2013

A suspension top link come adrift.

It is very, very unlikely to be a suspension part.
posted by Brockles at 7:56 AM on May 28, 2013

Sorry, but the only way you are going to figure out whats wrong with your car is to "crawl underneath the car when it's cool and try to find the loose part." You say that you can recreate the sound by wiggling the tail pipe around - do this when underneath the car and look for a loose or broken exhaust hanger or joint. It seems unlikely that a heat shield would have come loose, but if there's something else going on, who knows...
posted by mrrisotto at 8:01 AM on May 28, 2013

This might be a great time to invest in some $25 jack stands so you can get up under your car and look around. I'd check the fitting that holds the muffler and exhaust pipe in place (it's u shaped with some screws on my car) mine lost a screw and had similar symptoms. A plus side to having stands is that you can then change your own oil, that saves me $15/change per car around here. Autozone and the like have pretty regular 5q of oil + a filter for $15 sales and I'll get enough for 4 oil changes and be set.
posted by julie_of_the_jungle at 8:04 AM on May 28, 2013

This might be a great time to invest in some $25 jack stands so you can get up under your car and look around.

In particular, do *not* crawl around under the car with only the spare tire jack holding it up. They are far to easy to accidentally knock over. You want to jack the car up, put stands underneath, then lower the car onto the stands before going underneath it.

Don't use concrete blocks, either -- in general, people overestimate the strength of them, they fail easily under point compression loads.

I agree with Brockles that it's very unlikely to be a suspension part, because you can recreate the noise by shaking the tailpipe.
posted by eriko at 8:17 AM on May 28, 2013

Best answer: Had this exact problem, and it was the exhaust heat shield. Happened at very low idle speeds, which is when I was stopped AND had the brake on, which made me think it was a brake problem. Got it fixed at the next oil change for, like, $25.
posted by MrMoonPie at 9:12 AM on May 28, 2013

Best answer: Also just fixed this on mine and it was the heat shield on the cat. BenPens list sounds pretty spot on. Always block the tires when you crawl under a vehicle for safety.
posted by goat at 10:00 AM on May 28, 2013

In lieu of jack stands or ramps I've performed many a reapir like this driving one side of the car up on a curb.
posted by Mitheral at 10:13 AM on May 28, 2013

Happened to me a couple of times and there was a broken weld in both instances. I think I got hosed for a new muffler in the first case but the second time was more of a road emergency and the garage didn't have a replacement muffler, so they just did a re-weld and it's been great for nearly a year now. The sooner you get it looked at, the better.
posted by bonobothegreat at 11:26 AM on May 28, 2013

2nding erico. BE CAREFUL if you jack that beast up to crawl under! Use jack stands or ramps, make sure the shifter is in "park" (or first or reverse) and apply the emergency brake as hard as possible.
posted by drhydro at 10:09 PM on May 28, 2013

Response by poster: Thanks for all the responses - rest assured that I am terrified by even the thought of getting under a car supported by concrete blocks or a jack (do people seriously do that?!) so I will be appropriately paranoid when conducting my investigations.
posted by primer_dimer at 5:06 AM on May 29, 2013

Response by poster: Update: it was the heat shield - one of the bolt holes had rusted through and it had dropped down onto the exhaust. Slid on a washer and all is well. Thanks for all the suggestions, best answers all round to those who guessed heat shield!
posted by primer_dimer at 6:29 AM on June 2, 2013