dilmah

I've got the same problem on my 04 Impreza GX. The sound comes from the passenger side (I live in Australia - so drivers side is on the right) and is only noticable at initial startup and occasionally when starting off from a set of lights (or revving the engine in neutral). I've taken it back to the dealership twice now and they say it's air in the cooling system. They've bled the cooling system and replaced the radiator cap, but the problem is still there. I'm taking it back near the end of the month and hopefully they'll replace the heater core. Hopefully that's where the air is leaking in from. They've said that this is not a major problem (i.e. wont cause it to overheat), but it's just annoying :-\. Not sure if yours is the same problem, but something to consider.