well... take it for a run
then park it up... let it cool a bit so you can actually touch stuff lol
pull the easiest plug you can get to
what is it firing like
to be honest i wouldn't use bosche... we're japanese cars... so we use japanese plugs... well that's my opinion anyhow heh
you still didn't mention when exactly the muffler explosion happens?
on boost.. off boost.. acceleration... deceleration... idle?