Engine Rumble

The strangest thing.
I was driving fine, parked up and switched the engine off for around 15 minutes. When i switched it back on the engine wasn't ticking over very well whilst also beeing louder and rumbeling, i tried switching off and starting several times but nothing. So 15 minutes later i thought i'd have one last go. Started it and it was fine, so i drove around. The next time i tried to start it again, it did the same. This time i drove it for a liitle while and as it was running very badly the engine made this almost like coughing sound to realese something and again back to normal. But of course it did not stay that way. Can anyone please help.