Rattle on acceleration under load and firework type smell

Hi

Had my head gasket changed a couple of weeks ago and I have a rattle under load (it was there before but not as bad) also in the last day or two when the car is driven and it is worse when its been taken high into the rev range I get a strong smell of fireworks, I think it is coming from the exhaust but can be smelt strongly in the car. Do you have any suggestions?
Thanks