Other S60 Problem: Dump valve noise when lifting off throttle

[The Purifier]

Hi

I've noticed in the last few days when accelerating and then lifting off to change gear that my car (S60 2.0T) has started making a short hissing noise, in fact it sounds exactly like a dump valve although I didn't think the car had one? Thinking the noise was turbo related I've revved the engine while stationary but it doesn't do it then. The car is running fine apart from a slightly lumpy idle at times. I've owned the car for two and a half years and driven nearly 40,000 miles in it and not heard this noise before though

Would anyone have an idea what could be causing it? Or if it's normal? I've probably been quite vague so I'll happily provide more info if it helps

[dannyboynortheast]

it will have a recirculating dump valve, thats probably what you can hear. I can hear mine at times.