My 2007 xc70 was sluggish for the past couple of months. No changes were made. All of a sudden she is the peppiest she has ever been, but starting at around 30MPH there is a whirling noise that gets loud, so loud it is hard to carry a conversation. Then when you decelerate the sound gets lower until 25-30mph and you can no longer hear it....She has 110k miles on her, otherwise she is perfect..Question could it be the turbo? If so big$$ to fix? Is it ok to drive? Thanks much

 

Forgot to say the 'sound' is coming from the drivers side under the hood..