Hello.
I have a 2008 Volvo S80 2.5T 5 cylinder, automatic transmition and with 80k kms on the dial.
Recently I have experienced a buzzing sound comming from the engine, sounds like a loud bee buzzing.
Sound increases as I accelerate, not related to vehicle moving or shifting as just by accelerating when parked, with no movement it increases in volume.
It is not too loud but you can hear it and it is fustrating.
Any one outhere have an idea what this sound is?
Many Thanks!

 

Had the same problem, It was my breather box (PVC valve). I am not a mechanic but from what you describe its the same. Google Volvo breather box noise to compare the sound.