General Exhaust problems

[Damian99]

Hi i have a fiat Ulysse 04 plate, the exhaust seems to rattle and backfire when changing down the gears(when slowing down) it had a part exhaust put on before i bought it. Ive since taken it back bcos of the problem and they have put a new back box on, yet its not solved anything.

Has anyone got any ideas please?

Thanks.