I'm sure this has been discussed over and over but I did not feel like trying search for an answer since my mangina is aching tonight. When I accelerate or rev the engine I hear water behind the dash. I know it's going through the heater but how do I remedy this sound? I did read something on "burping"...explain. I suspect I may be low on coolant but radiator is full even when thermostat is open. Suggestions?