Humming sound when driving.

[Davo114]

Hi. I've owned my used 2009 Prius since January this year. Its in great condition and has only done 63000 miles. Over the last fortnight however it makes a distinct humming noise when driving. The sound seems to appear at around 35mph and becomes increasingly louder the faster I drive. I'm worried this might be a CVT transmission problem? The sound happens when driving in all directions, there's no vibration in the steering wheel or on the brake or acceleration pedal. I wondered if anyone might have any idea what it is please?

Thanks.

[BhxTrev]

Sounds like it could be a worn bearing, probably a wheel bearing. I had a worn wheel bearing on another car many years ago, which hummed. The noise got louder as I drove faster. If it is a wheel bearing, don’t delay in getting it fixed because it could collapse with deadly consequences!

[TonyHSD]

Or perhaps a bad tyre. 
These cars transmissions rarely goes wrong . Bearings or tyres are most common fault and can sound a bit bad