W203 water gurgling sound from behind dash.

[Orchid1]

I've got a 2004 W203 C Class and today as I haven't driven it all week decided to go out and turn the engine over and give it a few revs. Whenever I revved it I could hear water sloshing about just behind the dashboard.

I remembered I heard it happen before but had forgotten about it as it only seems to happen for a few minutes after I start the car.

I know it's probably just the coolant sloshing around on a cold start up but was wondering if it's something I should be concerned about because if you ask Dr Google I get directed to all sorts of scary websites and forums that mention head gasket failures and repairs running into large amounts of money.

I should say I only drive it about once a week (on a long 80 mile round trip on the motorway) and when I got it fully serviced last month at an independent they checked it all over and said everything is in tip top shape with it.

It's got 60k miles on it, only one previous owner who had full Mercedes service history.

Anybody have any thoughts? It runs completely fine, no other problems or anything out of the ordinary.

[television]

Water sloshing around or you can hear a water sound, if only on start up probably the heater box filling.