I feel as though the recirculation valve on my 150T is leaking or something. When the car is put under stress, i.e. 3rd gear at 20mph and floor the pedal, it makes a high pitched whirring sound. Uphill makes it louder. (really hard to explain) All the cars power seems to still be there though.

I've been having a look around the turbo and related hoses and stuff but can't work out where the recirculation valve is because I want to disable it to see if it's the valve thats making the sound.

So where is it?

do you mean EGR valve

No, the recirculation valve for the turbo.

I have the same issue since day one. It's like high-pitched farting. Made several trips to the garage - all the pressure was fine, I was told it's nothing to worry about. But it got worse with TMC kit so I can now barely stand it when it does it (does not do it every time though).

Looks like it's the dump valve indeed - I tried with another one (same car) and it was fine. I am currently waiting for a new dump valve to replace the current one.

Another member had the same issue and replaced it, but didn't solve it for him so he got rid of the TMC kit. I am pretty sure the kit has nothing to do though, it's probably a faulty valve and the increased pressure just makes the problem worse, which is pretty logical.

You can easily locate it, it's a T-shaped hose on the top-right corner of the engine. The actual valve is inside the hose. There are two or three hoses, gathering in it. Indicated with a blue arrow on the image (the red circle is not from me).

It's officially called air by-pass selenoid valve.

There's two plugs down there, and i've been told one of them disactivates the valve. So i'm gonna go and unplug one of them and see what happens.

Doesn't sound like a good idea. I'm not very technical, but since the idea of this valve is to release excess air, disabling it may damage the turbo...

I unplugged one of them and it sorted the problem out! So it must be a faulty valve! Car sounds awesome right now, chattering away, but as you said it may be bad for the turbo. Check Engine light came on