I used the search button!!!!!

Background:
I just replaced my drivers side injector o-rings and cleaned up all the hose routing for my procharger. I also cleaned the TB with a shot of TB cleaner. My car runs great, I let her idle for ten minutes, checked for leaks and then took her for a short spin. When I parked her, I turned her off and 2 seconds after the engine is off (no dieseling or any symptoms) the car made a sound like a kick drum being hit. It only made one thump, back near the muffler and that was it. Started her up, turned her off and same noise. 4 out of 5 time she did this. Nothing horribly loud like a back fire, nothing violent just a thump from the muffler, allmost like a fart!
What gives? Ideas?
TIA

 

Could it be the heat shield from the cat warping from heat and then "popping" back into shape? Have you tried the process while the car is cold before the cat has a chance to heat up? Give it a try from dead cold and let it run for longer and longer times between stops to see how long it takes to occur.

 

Ill have to listen. Thanks for your help. Really sounds like its from the rear allmost like its congestion moving from the engine and then out. What would cause a mild sounding back fire. The car did it today after work. Let her warm up for 8 minutes then drove two miles. temp was 160. turned her off and "poot poot" Again I was screwing with my injectors, just the o-rings but would this have an affect? Thanks again.