Gurgling sound on switch off

When I turn the ignition off I hear a long and strange gurgling sound (seems to be from right infront of me and close to me (right hand drive). Maybe a little lower and forward - yup, towards engine bay.

Just wondered if anyone has had it and can say "Ah ha... i know what that is"

I checked steering fluid and topped it up a bit.

Quarter tank of fuel.

Can't think what else would make a gurgle sound on shut down (and it wasn't my stomach).

Even the wife heard it from the passenger side and she isn't paranoid like I am about every little sound a vehicle makes.

No never, but I believe air can become traped in the heater matrix as that is the highest point of the cooling system and therefore with give a gurgling sound.

as above low coolant level expansion tank level isnt necessary level in system

Thanks guys - sorted now with a bit of flushing etc - cheers