| Just had a new cat fitted to my wifes 1998 1.4 Saxo. It was fitted at a discount exhaust place as the cost was very good. Howver the new cat now "booms" especially on the overrun. I will take it back but any ideas. I can't think what could cause this. there are no leaks. Ideas and comments appreciated.
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                    | Afraid this often happens with cheap after-market systems.  They are not made of as substantial material as the OEM ones, and not necessarily 'tuned' to remove the resonance - as a result they tend to 'boom'.  It will probably lessen as you get some miles and soot on it.  Worth a check back if it's particularly noisy to make sure it's not touching the car somewhere, or there isn't a bit of a leak. 
 
 RichardW
 
 Is it illogical?  It must be Citroen....
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                    | Thank you. Its true that it seems to have got quieter over the past two days (or my ears have become accustomed to it) I will give it a week to see if it improves further. Sometimes the cheapest is not the best.
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