The last few weeks, I have been hearing a whistling/whoosing noise on WOT when going to pass someone.

It is coming from the right side of the engine compartment between the turbo and firewall. At least that is where it sounds like. I have no clue how to verify that driving it.

Can anyone point me to what to check?

 

You may have the same problem I'm having. Either one of your boots on the hot side of your intercooler or the plastic piping on the cold side is leaking.

 

Feel the boot coming out of the turbo for a tear and oil residue. They can crack sometimes on the underside where you can't see. A deep 11 mm socket and you can have it off for a full inspection. Once off, pinch the hose in half and look for the crack. Also check the lower one at the intercooler.

 

Sounds like an up pipe leak if it's back by the firewall. look for black soot on the firewall.