02 chevy tahoe weird sound from engine bay

[norwegiantahoe]

Hi i recently bought a 2002 chevrolet tahoe 5.3. I just noticed a sound coming from the engine bay at idle.
It only occurs when car is at idle and when the heater is on, and stops right away when i stop the fan. happens both when a/c on or off.
The sound is coming from under the hood at the passenger side it seems like.

I will try to describe the sound the best i can, it goes like Brr for a second and then a slight woosh sound after. it does it every 5 seconds or so. i have not noticed it earlier and just wondering what it is.

If it helps i can try to record it tomorrow, and upload to youtube so you guys can hear the sound.

Hope someone can help me find out the problem, if it even is a problem.
Thanks.

 

[TURNz]

Is it the A/C clutch engaging and disengaging, like it does when you use heat for the defroster?

That wouldn't only happen at idle, but you might not hear it above idle.