I have just had a new exhaust including the cat fitted to my 1.1 Saxo, but it still makes a noise as if it had a big hole in it. But there is no sign of a leak at all and it sometimes goes quieter, like I would expect it to sound. Any help would be appreciated.
When the car is making its noise - put the palm of your hand over the tailpipe end. If you can hear gas hissing then its leaking all right. On a ramp, look for black deposits on the pipe to silencer joints.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.