Q: Sloshing noise on startup

The first thing to do is check your coolant and see if you’re low on fluid. When you are low on coolant, air bubbles are created and these air bubbles will slosh through the dash because the heater core is located there.

In today’s modern vehicles, it doesn’t matter if you have the heater turned on or not, the water is constantly circulating through the heater core. The only thing that keeps you from getting heat inside of the cabin is that the blend door to the heater box is closed. When you turn the heater on, it opens that blend door and the hot air goes through the heater box, allowing the air to come out hot.

That being said, your problem could be simply low coolant levels. Also, have your refrigerant for the AC checked as well because if it’s low on refrigerant, it can make a sloshing sound too.

If you need help with these checks, contact a certified mechanic who can ensure your coolant is topped off and diagnose the sound firsthand.