I had my mechanic change my serpentine a month back, asked him about the sound and he said it could have been my belt was bad, but it's still making this sound. I asked him at the time to test drive it and check for any problems and he said nothing was wrong and car rides fine. The car does ride fine except for this noise.

Here's a vid I took..

 

There is a problem ,give some gas .

 

What?

 

I think he wants to hear how the sound changes when you give it some throttle. Does it get louder when you turn the steering wheel?