Q: Rattling noise inside engine when AC/Heater/Air on

asked by on January 02, 2018

Hi there!

For the past maybe year or so I've been having this weird rattling under the hood that happens when either the AC, Heater, or if I'm 'circulating' air (not on hot or cold air). The noise appears when the car is turned on after being used (not cold) for about 5 seconds and goes away. I had a listen to where the noise appears to be coming from and it sounds as though it's coming from the top left corner behind. The sound almost sounds like a rock in a can being rattled.

Any help would be greatly appreciated! Thank you!

My car has 154000 miles.
My car has an automatic transmission.

You may have a serpentine belt or tensioner issue and may need to have them replaced but first should have a mechanic like one from YourMechanic diagnose the problem to verify the noise.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

What others are asking

Hi - Knocking noise

Hello. If there is a knocking noise then it may have some bad fuel or it may be another failure like an internal engine problem or a bad sensor. I usually start the diagnostic process by scanning the computer for...

Huge coolant leak in 2003 Ford Focus first overheated, temporary repair is now smoking with a huge new leak

If you have overheated the engine due to loss of coolant from a leak you may have blown the head gasket and need major engine work. Recommend getting the systems checked to see if the engine is damaged and need...

Sensor problem? Transmission overheating

Hi there. Your Focus has what is called a dual-clutch "automatic" transmission. Mechanically, it is a manual transmission with 2 clutches and servos, and other electronics used to handle the clutches and shifting such that it acts like a classic...

Sputtering and lack of power when accelerating

Whenever your Check Engine Light is on and a code is set, the ECU resorts to base settings and mapping just to make sure the vehicle runs, but not necessarily the to help the car run well. In this case,...

Clunking in rear

Hi, when does this occur? There could be multiple things involved. If it happens when you shift from reverse to drive or vice versa, the gearing in your rear differential may be misaligned creating a larger than normal gap between...

Can't shift out of Park

Hello. In this case, there can be many possible culprits, ranging from a failed brake light switch to a broken shifter mechanism. Since you noted that you have a faulty column shift handle, it would most likely be best to...

Steering Angle Sensor

Your vehicle has an electronic vehicle stability control (VSC) system. The VSC system relies on data from the steering angle sensor to keep the vehicle on the intended path during an emergency maneuver. Inasmuch as this is a valuable vehicle...

Battery saver light on but diagnostic check by mechanic shows no issues and the warning started appearing after new battery instal

Hello, thank you for writing in. There are parts of the charging system, like the alternator output, that are monitored directly by the computer with sensors. However, there are enough sensors in the system, the aspects that are not directly...

What does the Safety Belt light on the dash mean?

Seat belts are by far the most important safety feature in your car. They’re deemed absolutely critical, and are actually the only “lifesaving” apparatus installed in the car. Even your air bags aren’t rated as “lifesaving” by the US government,...

Related articles

A Buyer’s Guide to the 2012 Ford Explorer
Over Over 20 years ago, Ford changed everything for the American car-buying market when they introduced the first generation of the Explorer. Today, the 2012 Ford Explorer continues the evolution of modern large SUVs with a number of updates, including...
2012 Ford Mustang vs. 2012 Dodge Charger: Which One Should I Buy?
Technically these two vehicles have wildly different classifications: compact for the Ford Mustang and large car for the Dodge Charger. However, who would consider either one anything other than a muscle car? These cars are meant for speed, fun, and...
2012 Ford Focus vs. 2012 Mazda 3: Which One Should I Buy?
Compact sedans and hatchbacks provide a great ride on a budget, with the evolution from a stodgy, unattractive exterior (and interior!) to a more fully-featured trim set and exterior design. Driving enjoyment is improved throughout the class, which are known...