I have a 2000 subaru Impreza wagon with 42,000 miles on it. I'm guessing this problem started around the time that the radiator fluid was flushed and replaced because its sounds like bubbling from the engine area which I'm assuming is radiator fluid.
The problem seems to only happen when I am in a low gear and at low rpms I hear a bubbling noise from the front of the car. In higher gears 3rd and up or at RPMs greater than 2500 I don't hear the sound. I'm guessing its something in the radiator Air bubbles or something is this a major issue or will it cause damage to the car?
The gurgling sound is the coolant boiling in the radiator. You may have a bad fan not allowing the coolant to cool. If you keep driving like this, you WILL damage the engine.
Do this: Ensure there is nothing blocking the radiator front (leaves, trash, ect)
Make sure that there is coolant in the system. With the radiator cap off, run the engine and watch to see if the coolant is circulating through the radiator.
When the engine warms up, the thermostat should open up in about 10 mins. You should see the level of fluid in the radiator drop. If it doesn't, then it's possibly a bad thermostat. When the coolant gets hot, the fan should come on. If not, then it's either a bad fan, switch, wiring, relay.
REMEMBER TO OPEN THE RADIATOR CAP ONLY AFTER THE CAR HAS COOLED - do it on a Sat morning. ALSO WHERE EYE PROTECTION AND STAND BACK FROM THE VEHICLE EXCEPT TO CHECK THE FLUID LEVELS. You'll hear the fan turn on; you don't need to stand there and watch it. Safety first!