2001 bmw x5 - whistle sound coming from under the hood when accelerating!

[bosanci28]

i have the 2001 bmw x5 ,4.4l
and for few days now ,for some reason i dont have a clue and i cant find from where is coming from,there is a whistle sound coming from under the hood,when accelerating or when i put in drive to go,based on how much i push the gas the sound goes higher,but i think from 20-25 mph and up i cant hear it no more.

here is a link to a small video:
video one:
here

and video two
here

anyone had this problem?,i just cant find where the noise is coming from!
it maybe from somewhere related to air ? vacuum...

also sprayed some belt stuff to see if is from the belts ,but it was still there the sound,checked all fluids ,all okay.

at this point dont know where else to look !

thanks for any advice!

regards,
bosanci28