My car has starts to hum at certain speeds. It's an automatic but when it's in
fourth gear it starts to hum.  Do you know what this could be?

J.

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What make, model, and year car is it?
Richard

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Sorry its Mazda 6, sedan 2005. It hums when I'm up to 40 or 4th gear...

J.

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Does it change with throttle angle or vehicle speed (remaining in 4th)?
Richard

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Yes, if I go passed 40 it will start to him pretty loudly.
J.

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If you swerve gently back and forth does the humming get quieter or stop?

If so, it's a hub bearing..
Richard

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You are amazing! I found it was the hub bearing.    I went to a mechanic who tried to take advantage of me and I was able to break down the symptoms and possible issue.   He all the sudden took me seriously.

J.
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That's what I'm here for...

:)