As per title - rather than try to describe it I've attached an audio file. You'll need to turn your speaker up and the sound is at about 8 and 13 seconds in.

Thanks
Nick

 

Sounds fine to me, even the stock recirc makes a little bit of noise.

 

Driving around town you'll hear nothing but the forge is stiffer than OEM and will produce more chatter as I'm not sure all is recirculated depending on the boost its dealing with and you will get a slight blanked effect.