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Loud Humming From the Engine

After I took my Ford Focus 2011 to the dealership for a free oil change I noticed a subtle, low hum coming from the car when I hit speeds past 40mph. At first it sounded like the engine of a louder car driving near me so it took me a couple days to realize that it was actually my car making the noise. I intended to bring the car right back to the dealership to complain about this but I kept getting preoccupied with my studies for my summer courses. It’s been roughly 3 weeks now and the low hum has gotten a lot louder now and can be heard over music.

The noise begins when I approach 40mph. The noise is probably at its loudest at speeds of 40mph-70mph. The noise is made even when I am not stepping on the accelerator or using the breaks. I haven’t tried putting the car in neutral at those speeds. Does anyone have an idea about what might be causing that noise? I want to have some idea about this before taking it back to the dealership this week, although I don’t really trust the dealership since my car seems to manifest a new problem after each visit. I’m hoping that it’s just something that isn’t major or expensive to repair.

Possibly an underbody plastic panel they failed to tighten down.

yep to above post

you waited too long tho, minor things can become major if not addressed.

How would I check to see if that’s the case? If it’s a problem that doesn’t require too much skill then I’d like to fix the problem myself since I don’t really trust the dealership mechanics.

Yeah, I knew I waited too long but it was difficult to find time to get my car out to the dealership during the semester.

There are too many could be possibilities. If you are covered by a warranty, let the dealer fix it. Could be a bearing of some sort or another.

Does it rise in pitch as the speed of the car increases? If so it could be a wheel bearing. But I’m puzzled as to why it doesn’t start until 40 mph. Insightful may be right. The wind blowing through a loose panel can start it vibrating.

Food for thought . . . it could be a failing wheel bearing

In that case, the dealer can’t be blamed

Whyen something like this happens it’s best to get back to the repair shop ASAP.

Now they can claim that they didn’t hear anything after the oil change, and they will presume that it is not that important because you waited three weeks.

If you could drive it onto some ramps, you might be able to wiggle things around and find a loose panel.


Wheel bearing sounds likely, does it get louder as you speed up or change in pitch when you turn. Both of those symptoms are common signs of a failed wheel bearing.


It doesn’t change in pitch when turning. In the range of 40mph-70mph it seems to sound all the same.

It’s sounding more & more like insightful may be right. The air flowing by the loose panel causes it to vibrate at its resonant frequency. Resonant frequencies tend to remain at a constant pitch regardless of varying wind speed.

loose heat shield?

If your free oil change is pre-paid maintenance the service may have included a tire rotation. Some small vehicles are prone to a wear pattern on the rear tires called cupping if the tires are not rotated on schedule.

When cupped tires are moved to the front of the vehicle they are much noisier than in the rear. It can sound like a noisy truck with off road tires is driving next to you.

Inspect the tires tread on the inside edge for a series of high and low spots. Also double check their work, open the hood and check that the oil cap is on and the air cleaner housing is closed. Look under the vehicle to see if the under engine cover is hanging loose.

Since the frequency remains the same throughout the speed range posted, I too would suspect a resonance going on. You might try putting the front end of the car on ramps (rear wheels chocked, parking brake engaged, engine off… SAFETY FIRST) and checking underneath. There are heat shields that can and sometimes do become loose and vibrate at specific frequencies. One known for this is on the Catalytic Converter. They’re typically spot welded or tack welded to the converter housing, and when one or two of the spot welds break free the shield rattles.

If it does turn out to be this, the accepted (by state inspectors) permanent repair is to wrap a large worm-drive hose clamp around the converter and the shield to hold it from rattling. Worm type hose clamps only cost a buck or two apiece, are available at any hardware store, and can be strung together if needed to get the length. And they’re stainless steel, impervious to the undercar environment.

Post back with how you make out. $25 for a set of ramps and $5 for hose clamps is a heck of a lot cheaper than any shop, and that’s often all that’s needed.

Okay! Thank you so much for all your valuable input! I’ll try and see if I can borrow ramps tomorrow to check everything you guys said! I’ll post back with how things turn out!