Hi all,

For a while now I have been getting a rattle coming from what seems like underneath the vehicle when accelerating. The rattle only happens at 2k rpm. My initial guesses were something to do with the exhaust hanging loose or one of the heat shields coming off.

Today I took it to Halfrauds for a free exhaust and catalytic converter check where they said the catalytic converter needed renewing, quoting £570. Furthermore, on the drive home the rattle seemed to disappear, probably as they poked at and shook the exhaust a bit. 

Do you guys reckon the catalytic converter is the problem and can cause the rattle as described above? Also, do you think the quote is reasonable? I thought it seemed quite high...

Thanks in advance.

Just checked the price for my Fiesta on https://www.cats2u.co.uk/3596-10#/type-catalytic_converter/fuel-petrol/year-2017

Quoted £220 inc VAT

£177 for your year.

I wouldn't replace a cat just for a rattle, would wait until it's blowing or fails emissions test personally.  For £570 I bet you could get a full stainless system fitted though!

 

Thanks for your replies.

I will probably follow the advice of @TomsFocus and wait until its blowing or fails its MOT emissions test in Nov. If neither happens, the rattle may return but I can probably live with that until the cat gives out.

Did they actually show you the problem eg took you under the car and demonstrated the rattle showing you where it came from?  If not I am sceptical. Like others say I wouldn’t replace until you have to. 

No unfortunately not, they were pretty ***** to be honest. They simply said the catalytic converter was excessively damaged. I technically still don't know where the rattle is coming from. I had narrowed it down to the following (in likely order):

• Exhaust hanger loose and exhaust is rattling against something. (Probably not since it would rattle the whole time and not only at 2,000rpm).
   
• Heat shield is loose and is rattling against the exhaust. (Probably not since it would rattle the whole time and not only at 2,000rpm).
   
• Something is loose inside the catalytic converter which only rattles at 2,000rpm.

I had an escort where the exhaust would rattle / vibrate only at a certain rpm, there was a heat shield welded to the underside of cat. On one corner the heatshield weld had cracked and come adrift. A blob of weld fixed it.

I'd get under and make sure there's not a heat shield loose

Is there not something that loosens and breaks free inside a cat converter? A friend had a VW Golf a couple of years back when revving, his had an awful rattle from the Cat. Didn't do any damage or cause any issues but it was annoying to say the least.

Anyway, he is currently a Tech for BMW (🥴) and I am sure I remember him saying when they do that the cat is on the way out and will fail sooner or later but again, remembering correctly, apparently the rattle can be stopped by finding the exact point of the noise, drill a small hole and put a stainless self tapping screw into it as a cheap botch it fix. 

He never fixed it, traded the car against another one.

22 hours ago, Bobr said:

Just checked the price for my Fiesta on https://www.cats2u.co.uk/3596-10#/type-catalytic_converter/fuel-petrol/year-2017

Quoted £220 inc VAT

£177 for your year.

I would guess labour cost etc would nearly double the price of the parts.🤨

The actual cat is a honeycomb, once that starts to break down there's no saving it, but it might still last a while before it needs replacing.  Metallic rattles are generally caused by baffles in silencers (metal plates welded inside to reduce noise) that come loose when the weld breaks, it's these that you can hold still with a self tapper.

If you do have to eventually have the cat replaced, don't let the garage keep the cat as they'll be rubbing their hands, so keep it yourself and take it to a scrap recycling yard that buys cat's, be surprised how much it's worth, son works in such a yard and the cat's that are took in an weighed is shocking, what's even more shocking is most of the cat's are fine and garages rip customers off by telling them their cat is shot, when it's not! This scam has been going off for a few years now, it's a win/win with the garage who falsely tell you the cat is tattered when it's not, I mean how can Mr. Average Motorist say it's not tattered, they just trust the garage but what they don't realise is that they are being ripped off.