Mysterious "sloshing liquid" sound in the dash

Whenever I start my car and put it in gear, I hear the sound of liquid sloshing around as if there were a tub of water just behind the stereo. I can hear it for the first minute of driving (when I accelerate or decelorate) and then it goes away. The sound returns after the car’s been sitting for a while. What’s going on?

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It could be an air pocket in the engine cooling system. The noise you hear is the coolant being pumped through the heater core when you start the engine.

Make sure the radiator is completely full and that any air is bled from the system. Some vehicles have a special valve for this purpose.

Check out McP’s suggestion first and if that isn’t the fault, check to make sure the fresh air vent water drains (below the windshield) are clear.

Check the cabin filter(s) as well (if equipped).

One might think a sloshing sound in the vent area would be there all the time if they were plugged. Wind noise, engine noise, etc. can mask the sloshing noise.

Not many questions here can be answered without a vehicle ID.

Thanks for this. I’ll check the coolant levels. Also, forgot to mention it’s a 2007 Chevy HHR 2.4 LT.

An air pocket in the heater core would be more of a gurgling sound. If you are really hearing a sloshing sound, then it is very likely water trapped in the AC evaporator drain pan. This would be because your AC drain tube is clogged. Find it and check it.

You may check under the hood as I had a trough that the wiper mechanics resided in. The drain holes were blocked. It filled up and ended up leaking into the passenger area and ruined the carpet in my caravan. Good luck!

It may not be a liquid sloshing. My 04 Lincoln Towncar has that noise which turnes out to be the doors activated by vacuum to direct the heater/AC flow. Try different settings of direction and see what happens.