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My Car Hums When I Want It to Sing

We have a 2001 Mazda MPV minvan with 150K miles on it, and in the last month it’s begun to hum at various speeds. It’s not a road/tire noise kind of thing, because when the car is colder, the hum can be heard still. When it first started happening, it was real occasional, but now it’s pretty regular; when it happens, and the road is clear, a quick tap of the accelerator usually gets rid of it until our speed drops. Doesn’t seem tied to any particular turning or bumping or other car movement. Any ideas?

It’s a long shot, but the solution is cheap if I’m right. You may have a failing U-joint. This is an easily replaced, cheap part that might be your problem. If the joint has one bad bearing (of four per), acceleration may cause the u-joint to misalign slightly and create a slight vibration and the humming noise you are hearing. Tapping the accelerator could be allowing the joint to go back to it’s normal position, until as you say, you slow down and then have to accelerate again.

Thanks for the tip/thought. I’ll check it out – one follow-up. Would this be a possibility even at idle? The humming used to be solely when we were moving at speed, but now the humming occurs when the car is first started and idling (but the humming at idle tends to go away as the car warms up, and only happens at various speeds, which very much fits how you described the action above). Thanks again for your insight.

Have you tried listening under the hood to see where it’s coming from?