Has my Volvo caught a cold?

[Raddors]

After work last night parked up and locked the car as normal, then had to attend to the christmas lights around the porch. Whilst up the ladder faffing with the bloody things I heard a human sounding "cough" that scared the st out of me and I nearly fell off the stepladder, upon investigation it was the car!

About 4-5 minutes after turning off the ignition and locking the car it lets out this pathetic little cough from what sounds like the engine bay? Anyone had any experience of this? Car is a V50 D5 '08.