If your car heater is making a strange noise, it’s likely that the fan or heater core is broken or blocked. Other causes could be leaking water into your car from outside, or a leak in the heater core itself. If you notice any of these issues, it’s important to take care of them quickly to avoid further damage to your vehicle, and possibly save yourself some money in the long run.
When you start noticing noises coming from your car’s heater system, ask yourself what kind of sound it is. Is it a new sound? Can you tell where the noise is located (dashboard vents, under the hood)? It could potentially be several different things—a broken fan motor; a faulty thermostat; leaking water from outside; or even a leaky heater core—and knowing what type of sound you’re hearing can help narrow down what could be causing it. The only way to know for sure will be to have an expert inspect and diagnose the issue.
Heater fan is broken or blocked.
The heater fan is a small motor that circulates air around the car’s cabin. If this fan is broken or blocked, you’ll often hear a clicking or fluttering noise. The most common causes of this are debris blocking the fan or it is unable to spin due to broken blades. The location of the heater fan within your car will vary from model to model, but generally speaking it would be located behind the glove box, under the dashboard or behind the front bumper.
Fan is leaking water into the car.
If you hear water splashing, it could mean there’s a leak.
Leaky heater cores are relatively common. And if your heater core is leaking, the fluid that normally runs through it will be dripping into your car instead—and if your heater core is leaking, that fluid is most likely coolant. Coolant has a sweet smell, and since you’ll notice the noise only when the heater is turned on and running, chances are you’ll be able to use your nose to diagnose this problem: You’ll likely see steam or liquid coming from somewhere near the fan or below the hood (possibly near where the engine meets the firewall), and when you follow that trail of steam back to its source, you should see some sort of puddle or dark spot on or under the floor where coolant has already dripped out. Usually it’s not a ton of liquid; often just enough to leave a small puddle in one spot before evaporating again.
If all signs point to an antifreeze leak in your car’s heater system as being responsible for that mysterious sloshing sound whenever you turn on your heat, you have three options: 1) stop using heat until this gets fixed (which would seem like an obvious choice for many people); 2) continue using heat while waiting for this issue to get fixed (which would seem like an obviously stupid choice for many people); 3) call up a mechanic and ask them which option they’d recommend (which would seem like an obvious choice for even more people).
The heater core is leaking.
If your heater core is leaking, your car’s cooling system might be compromised, which can cause serious engine damage.
What happens is that the coolant gets transferred from the radiator to the heater core through a series of tubes. After flowing through the heater core, the coolant is then returned to the engine to help keep it from overheating. If these tubes are cracked or clogged due to corrosion, there’s likely a leak and you may have to replace your car’s heater core.