What's that noise?

SlyReaper

SlyReaper

SlyReaper

Soldato
Joined
26 Apr 2008
Posts
6,653
Location
Bristol, Old Blighty
My car has started making this metallic grinding noise whenever it's revved to about 2500rpm. It makes the noise whether it's in gear driving along, or in neutral/declutched with me revving the engine. If I rev higher or lower, the sound goes away.

Any thoughts? The oil level was well below the minimum, but I topped that up and it's still making the noise.
 
Nothing to do with brakes, like I said, the noise is dependent on engine revs, and appears whether I'm moving or not.

The exhaust is less than a year old, so I'll be annoyed if that's the problem. How would I check the heatshield or silencer?
 
Oil below minimum isn't good. What car is it? It's either burning it or it's leaking.

Sounds like an exhaust heat shield though as mentioned above.
 
It's a fairly ancient vauxhall astra, from the year 1993. 1.4l petrol.

It did cross my mind to wonder how the oil got that low. I'll check the level again tonight.

I'll have a look after work to see if I can spot anything that looks vaguely heatshieldish and see if it's loose.
 
Knackered or nearly knackered bush or mount resonating at that particular amount of revs, exhaust mounts, engine mounts, suspension strut tops?

Nailing down where the noise is coming from will help as mentioned above
 
SlyReaper said:
Nothing to do with brakes, like I said, the noise is dependent on engine revs, and appears whether I'm moving or not.

The exhaust is less than a year old, so I'll be annoyed if that's the problem. How would I check the heatshield or silencer?
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Jack car up, bang along the exhaust with a bit of wood or rubber mallet, listening for creeks and rattles, also give it a push/tug side to side. Inspect the exhaust mounts for corrosion or worn rubber bands if present.

With heat shielding, just give it a good yank/tug and listen.
 
mattyfez said:
Knackered or nearly knackered bush or mount resonating at that particular amount of revs, exhaust mounts, engine mounts, suspension strut tops?
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Those words. They make sense when I look at them one at a time. In a sentence, you may as well be speaking Mandarin. :p
 
Okay, I think I've narrowed it down. The noise seems to be coming from the engine bay, and right now, the chief suspect is this light grey piece of metal fore of the engine.

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Pretty sure it's an exhaust system heatshield; it covers the exhaust output pipe from the engine, but without actually touching it. When I pulled that piece of metal outwards a bit (it was in contact with another thingy), and revved the engine again, it didn't make the noise at 2500rpm. I mean, it still sounded about as unhealthy as you'd expect a 22 year old car to sound, but the tone of the bad noises did seem to change. The real test will be if I can drive it to work tomorrow without the sound reappearing.

Of course, I fully expect the plate to gradually sink downwards and touch the thingy again, at which point, the sound will return. Any ideas how to make this "fix" more permanent? I'd cut it away if I could, but I expect it was put there for a reason.
 
Scrutinize said:
Didn't think there were many of those era 1.4 astra left. They had all gone pop or rusted out of self respect.

Most likely heat shield.
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There aren't many. Haven't seen another one on the road for some years. It passed the point of economic repair and service a long time ago, so I've pretty much just been keeping it going out of sentiment. Its name is Ketchup.
 
It is just a manifold heat shield and many times I have bent them with pliers to stop vibration or taken it off completely with no issues.
 
SlyReaper said:
There aren't many. Haven't seen another one on the road for some years. It passed the point of economic repair and service a long time ago, so I've pretty much just been keeping it going out of sentiment. Its name is Ketchup.
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Has it gone a delightful shade of pink or have you polished it back up? :p
 
Stormster said:
Just rip it off if that's what it is, it will hardly make any difference IMO.
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That's just what I did with my old fiesta, the back box shield was fubar are so I managed to get a bit more life by putting a few holes in it and tying it up with some wire cable, but ended up just ripping the heat shield out as it still rattled.
 
You can always check yourself, the throttle cable (top left in your picture I believe) can be pulled under the bonnet too, no need for a 2nd person in the car.

If it's the heat shield, don't worry, either mend/glue it in the place where it's rattling with heat resistant (epoxy) paste, or even Gun Gum, or pull the heat shield off ( careful to not damage the rad while breaking it off).

Tbh your bonnet space looks very nice to work on, newer cars have so much plastic crap and are much more cramped, old cars ftw for a self mechanic :D ( forgetting the bolts and nuts that wont move or even break off due to rust :().
 
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Was going to say actually, if it's easy enough to remove the shield, and you can sus out where it's rattling you could bend/bash it in to shape with some pliers and a hammer, or even saw the offending part off if possible, leaving most of it in place.
 
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