There is a rattling sound coming from my exhaust at low revs don't now if it's blown as it does not seem to be hitting the bumper, the engine has been out and put back about a month ago what's your thoughts

 

I would say check and see if all the brackets are tight enough underneath.

 

Not had a look are they not rubber rings that hold it up

 

might be a loose heatshield. i had the 1 above the backbox break off and it was sat ontop of exhaust rattling for about 6 month. ive taken it off now. havnt bothered fixing it back on as it didnt seem to make the boot floor warm.