What Causes the Humming Noise in a BMW 3 Series at Low Speeds?
4 Answers
The reasons for the humming noise in a BMW 3 Series at low speeds are: 1. Influence of body resonance; 2. Abnormal wear of the wheel hub bearing. Taking the 2021 BMW 3 Series as an example, it belongs to the mid-size car category with the following dimensions: length 4719mm, width 1827mm, height 1459mm, wheelbase 2851mm, front track 1543mm, rear track 1583mm, fuel tank capacity 59l, and curb weight 1555kg. The 2021 BMW 3 Series is equipped with a 2.0t turbocharged engine, featuring direct fuel injection, with a maximum horsepower of 156ps, maximum power of 115kw, maximum torque of 250nm, paired with an 8-speed automatic transmission.
My old BMW 3 Series also had that low-speed humming noise before, sounding like a piece of paper stuck in the tire when driving. After struggling for a while, I found out it was caused by the run-flat tires—the sidewalls of the BMW factory-fitted run-flat tires were too stiff, causing resonance even with slight road imperfections. Later, I tried three methods: reducing the tire pressure to 2.3 bar helped a lot; swapping the front and rear tires revealed that front tire wear and peeling could also cause noise; the most extreme was spraying the brake discs with a hose—if it was really the brake pads dragging, the noise would disappear instantly. However, if the humming gets louder when turning, it’s probably a bearing failure and needs immediate replacement. My friend’s car kept going until the bearing disintegrated, and even the half-shaft ended up damaged.
Last month when driving my 3 Series to drop off the kids at school, it kept making a low-frequency humming noise like an airplane taking off at around 20 mph. It took two visits to the repair shop to identify the culprit: first, they lifted the car and ran it in neutral with no noise, ruling out driveshaft issues; then the mechanic used a stethoscope on the wheel hub bolts and found the right rear wheel bearing made noticeably harsh sounds. Ladies, pay attention to these three clues: 1) This type of noise changes pitch with speed like whistling; 2) If it's louder with windows down than up, it's almost certainly a bearing issue; 3) If it's especially noticeable on rainy days, check if the tire treads are packed with stones - last time my husband dug out over a dozen small rocks with a key and the noise disappeared instantly.
Over ten years of repairing BMWs, I've encountered hundreds of cases of low-speed abnormal noises, with early bearing wear being the most common issue in the 3 Series. There's a classic detection method: maintain a speed of 40 km/h and slightly turn the steering wheel left and right. If the noise increases when turning left, it's the right wheel bearing that's faulty; if it gets louder when turning right, then it's the left wheel bearing. Last week, I handled an even more peculiar case—the owner had just replaced the brake discs with aftermarket ones, and uneven thickness caused the brake pads to resonate. A reminder to all: if you modify the wheels and don't use hub-centric rings, the low-speed metal friction noise can be headache-inducing; a leaking CV boot can also produce a similar buzzing sound.
