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Q: Rhythmic moaning noise that starts at ~30mph and grows in intensity as speed increases - what could it be?

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Hey, I'm looking at possibly buying a car (the one I entered information for) from my friend. It's been used VERY lightly in the past year (which is kind of concerning). In fact, I have a pre-purchase inspection scheduled with YourMechanic for 12pm tomorrow (Wednesday, 11/8/2016) with Edgar (Repair Order #1430419).

The main thing I'm worried about is this noise. It's a... rhythmic moaning noise that starts at around 30mph and grows in frequency and intensity as I go faster speeds. It sounds like "wah-wah-wah-wah" if that makes sense. It's nonexistent if I'm not moving but revving the engine - which makes me think it's got something to do with the wheel system or transmission.

Anyhow, I have no idea what it could be, and figured I could both gather some information and give you guys some as well in case you need to bring extra tools to the appointment tomorrow.

My car has 160000 miles.
My car has an automatic transmission.

A: Hey there. This is a common sign of failing...

Hey there. This is a common sign of failing wheel bearing(s). A wheel bearing will usually fail due to pitting or small damage on the surface of the rollers or the bearing race. Both the surface of the rollers and the race is precision machined to tight tolerances and highly polished to allow the rollers to pass easily over the race with the addition of bearing grease for lubrication and cooling.

Over time the bearings will wear slightly, allowing microscopic pieces of metal into the grease. Bearing noise can sound a lot like a brake pad dragging or grinding. It can also sound like whirring, whining or humming depending on how much sound deadening material your vehicle has in it.

Bearing noise will always be dependent on vehicle speed meaning as you speed up or slow down the noise should change frequency or loudness. Cornering may affect the noise from a damaged front wheel bearing and is usually more pronounced as you make turns. I would suggest having the professional check the wheel bearings in person to determine if they are in need of repair.

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