This is my nephew's 99 GT 3800 N/A (totally stock) and this is the crappy video he sent does anybody have any guess's?

I have not looked at it or heard it myself I am going to their house tomorrow (1 1/2 drive there) to check it out for him

https://www.dropbox.com/s/yy2g5dzyllrlr26/IMG_6779.3gp

let me know GPF