Just the other day i noticed that the car all of the sudden started this loud thud noise as the car was running. No engine light came on which threw me off, but when i went around back towards the exhaust it soulds like when in idle the thud noise was intermittent. 1 to 4 thuds then it stops then it continues. Started the car up again and it wasn't doing it anymore. I haven't started it up again so what do you guy's or gal's think?