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My 2009 Honda Civic makes a humming/whining sound when accelerating if the weather is cold. it gets louder the faster I go.

However, once I drive on the highway, the sound goes away completely. The sound also goes away if I drive a little bit (at least 5-10 minutes) and then turn off my engine and turn it back on.

Any ideas on what could be causing the issue and/or what I can look for under my hood?

Thanks!

 
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You’ll need a second person to listen while you’re in the car, or vice-versa. Sounds like a worn pulley/bearing. It’s probably proportionate to engine speed so just revving at a stop should replicate the noise.

 
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Ok thanks. I’ll take a look.

If that is the issue (and it certainly sounds like it is), is it affected by the cold?

Is this something that must be fixed asap?

 
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Just tried to replicate the sound with a second person revving the engine while I checked under the hood.

I didn’t see or hear anything but it is warm outside and the car was driven about an hour before.

 
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Yes. Metal will heat up and expand, generally removing any points of excessive grinding or friction. Not quite scientifically precise, but that’s the general, sort of correct explanation. I’d get it done sooner than later but it’s probably not urgent.

Alternatively, it could be an accessory belt that is too tight, and then expanding when it warms up. If this is the case, treat it with more urgency.

 
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Thank you. How would I be able to tell if it’s the pulley vs. the belt?

 
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like yourself said, it happens when cold, not hot...
most likely a serpentine belt, put some water on them to see if it screeches

Moved thread out of the "Site questions/Concerns" - that section is about the site, not about your car...

 
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Take the belt off and spin the pulleys.

 
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This morning, the sound recurred. It didn’t start until I accelerate. It continues, albeit quieter, once the car is in park.

The serpentine belt is spinning and doesn’t seem to be cracked or broken. I can’t tell if all of the pulleys are spinning because it’s crowded under my hood.