Exploded Resonator Box

[R5-al 2 1 Cars]

Ive just got my car back from haveing a exhaust done and as soon as I put the ignition on there was a loud bang and a puff of smoke from under the bonet after turning it of quick I removed the rad to find a large peace of thr resonator box (size of hand palm)blown of the bottom rigt under the hole where it enters the plenum!! Its confused me I havent got a clue! Has this happened to anyone else? Also my car is only 90% finished so not on the road is there something I could have done wrong to cause this? Of is it just the cold makeing the plastic brittle?Any helf would be appreciated

[pugpete1108 62 1 Cars]

Mine blew along the seam when the car backfired, so I ditched it and blocked the hole

[GTI6BOY 29]

Also had one blow with a back fire on the motorway

[R5-al 2 1 Cars]

Thanks Must have been that then