Makes sense. That would indicate the sound is more likely coming from the heater core. But how cold are the nights where you live? Cold enough the AC drain area inside the car might freeze solid? The water that goes into the AC drain area doesn’t have any freeze protection. If so, that could explain why you don’t hear any sloshing until you’ve been driving awhile.
I’ve had air pockets in the cooling system on my Corolla that cause a sort of sloshing sound when the heat is on, but its not related to braking. Every car design is different though.
Only recently has the weather here dipped to the 30’s. Had this car for over 4 years now though and through some brutal winters. Never heard the noise before this.
If it’s in the 30’s there at night, probably wouldn’t freeze even if there was a pool of water in the AC drain area, b/c that area is inside the car, unlikely to freeze unless the ambient gets below 30. The fact you’ve never heard that noise in the winter before doesn’t disprove the idea though, b/c the drain might not have been clogged then.
If you know how to safely get under the car, it should be not much problem to find. It’s usually a sort of rubber plug with a short tube hanging from it, located in the vehicle’s floor pan, usually in the vicinity of the heater core (which is also where the AC evaporator is located.) Wear eye protection good idea whenever looking upward at something under the car.
We just had a similar problem. We took a week trip. We began to smell something not right. After we returned home we were cleaning the minivan and discovered the carpets were wet. In fact they were soaked. We put a dehumidifier inside and for days we emptied out gallons of water. We discovered it was the ac condenser behind the glove compartment, the hose was blocked, pouring water into the passenger side. My insurance company authorized the repair. It took the body shop 3 weeks to rip out the whole interior and replace everything as it was wet everywhere.
It wasn’t 6k, more like $1800. I only paid $400 deductable. I don’t know what clogged it. But the Toyota body shop had recently worked on a Rav4 with exactly the same problem. That’s why I let them do the job. They had to eliminate the stink so they kept pulling out stuff that was wet and damaged. The parts took more time to arrive than usual, each time they found more. Please stop trying to blame me. I’ve never heard of this problem in my life. The dealership was surprised also.
