Humming just started under the hood

I loved my 2009 Prius until this weekend. I just turned over 31,000 miles and now a loud humming noise has developed under the hood while driving. It has not been cold here and this doesn't start until I reach around 24 mph. It remains while the gas engine is running or I'm coasting with the engine off. The humming is there in D or in N and there no sound while turning. When I am under 24 mph the noise is gone. I have set up an appointment with my Toyota dealer for this week, but wanted to know ahead of time if any other Prius owners have had this issue. I want to love my car again and not be out of a lot of $s. Ugh!

 

Thanks to all! Turned out to be passenger side wheel bearing and thankfully covered under warranty. I am less than 6-weeks away from the warranty expiration and I just want to continue to love this car without a major expense so soon. Right now I do now that this is fixed & sounding good. But having driven for over 40+ years and almost every make of car I can't say I am not a little surprised by a wheel bearing going out at this mileage. Guess it's luck of the draw but still wondering if any other Prius owners had the same experience.