I had the same sorter noise but was about 2seconds after turning my engine off just a loud pop! Couldnt tell where it was from sounded like xzorst like a back fire pop!!!!Also (droning on now) was driving down A12 the other day and decided to give it some beans (as ya do) and there was three massive bangs from the underside of my car (s2rs) like back fires then cus i paniked like ya do came off and slowly went back on and been fine ever since! except that when i now drive the car and its warm if i sit around 2100rpm it pops like a bugger in any gear go above or below and its returns to normal! any ideas on any of these???