I've left my car parked from yesterday ay 4.30pm till this morning at 9am. After I started the engine, I let it idle for less than a minute and got running. Usually when the engine is cold and so it is outside (0C), I don't get over 2000rpm. This time though, without the fan blower on, I've heard some sounds coming from the heater matrix, so somewhere from the middle of the dash, like water brawling or something like this. It wasn't that loud though, but it was there. I'm usually driving with the radio on, so it might have been doing like this for a while without me noticing it. After about 2 miles that stopped. Should I be worried for something like air in the cooling system or a bad water pump? The expansion bottle shows the regular level, there are no issues there.

If you have no coolant loss, no overheating and the engine warms up quickly then there is no problem.

Fiat Puntos seem to do as you describe every time you drive them... dont think its an issue as such though.

Do you have air con?

Yes, I do have aircon.

Might find the gas is low. Normally get a whooshing or bubbling noise coming from the evaporator when it's dropped a bit.

Even if the AC wasn't running at that time ?

A/C pump runs all the time to keep the system lubricated.

Thanks! That makes a lot of sense! I will check my refrigerant pressure Monday after work.