To get the sound you're after you need to blank off the dump valve.

Now, this can be inadvisable depending on what turbo you have. The TD series turbos are tough as old boots and will take it without a problem. Early VFs won't like it.

The problem with removing the DV on a maf based ECU is you'll get maf reversion, which is basically where the Maf senses un-dumped air and adds fuel unnecessarily, which causes the car to judder when you lift off when the engine is under load. Usually most noticeable in 4th and 5th. You may also notice that fast gear changes aren't as smooth - the car lurches more with sharp throttle transitions.

The solution is to get a mafless ecu like the Simtek.

These issues can be driven around though, so a replacement ECU isn't essential by any means. The main concern is whether the turbo will tolerate no DV.

The sound is not wategate chatter btw that's a common misconception. It is compressor stall; if I understand it correctly, it's best to think of it as the compressor blades chopping up air coming back through the turbo.

Ns04 (Been there, done it)

 

Could this 'chatter' or 'flutter' noise be created by a dumpvalve? The reason I ask this is that I've just fitted a Forge recirculating dumpvalve to mine, and I get a lovely chatter noise when I'm on boost and I let off the throttle slightly. If I'm accelerating and the boost is pretty high.......if I let off the throttle suddenly it just goes pttsssshh, but if I just back off the throttle a little bit I get a lovely bit of ptssh tsh tsh tsh tsh! I just thought it was the dumpvalve opening & closing really quickly because the pressure of air being 'dumped' is right on the point of where the spring starts to give way sorta thing? I got no idea! All I know is it didn't do it before the dumpvalve, and now it does!

 

That sounds to me like your dump valve is not opening untill it has enough pressure to move he spring, you prob have quite a stiff spring.

so the boost is going back down the induction intake and ou through the turbo which is causingthe noise. i would either stop doing it or remove the dump valve for another one with a softer spring.

I could be wrong as you mightof guessed from reading above i am no expert but from what i have picked up on here it sounds to me like this is the case!

 

Possibly, but if it is, it's probably not doing it in the way you think.

It might be behaving as you suspect, although I'd suggest it's more likely that Murph is right, the spring is too strong and so the valve is not opening on gradual lift-off, so the noise you're hearing is most likely genuine compressor stall.