A new noise started today. When I slow start or slow down into lower gears the slowing down sound is accompanied with a whistle sound. The slower it gets the more high pitched and it sounds like one of the turbo whistles you get. This is a petrol nas.

When you take your foot off the throttle and the butterfly closes there's an increase in vacuum in the inlet tract. Maybe it's sprung a leak somewhere downstream from the throttle body.

Hi do you mean the induction pipes or internal after the throttle body?

There's a pipe behind the inlet manifold that looks like goes into the throttle body and looks kind of flat is that normal?

Which engine do you have? I can't really help with specifics as our Mk2.5 probably has a different engine but I meant a leak in the inlet tract between throttle body and manifold, including any vacuum pipes that connect in that area, might make a noise under high vacuum. It's just a wild guess though, it might be something completely different.

It's the 1.6 Duratec (so called) MK2.5. Cheers for any help much appreciated.

Is it possible it could be the belts? When idle I hear a small whine like hearing aids if I crouch beside the drivers wheel and the belts are pretty much near there. I'm due belt changes at 10000  and I'm near 93.

Further to this the whistle is getting more prominent I have looked at the intake pipes and no dice it's really hard to pinpoint where it comes from seems more like near the battery end it's weird although it doesn't affect it performance wise.

Still not able to track this down and the whistle seems to be more constant could be be related to the tensioner?