Hi all,

I've got a 125PS EcoBoost Fiesta with 16k miles on the clock (owned since new). Just this past weekend, during a trip to the Lake District, I noticed the car had started to make a bit of a whistle when lifting off the throttle.

It's a short whistle (~1 second) that can be heard inside the car even at 70mph. It happens in all gears and only occurs after getting the turbo up to speed and then lifting off the throttle. There is no noise during acceleration. My guess is it must be the turbo dumping pressure (although no dump valve), but I've never heard the car making this noise before - there was a some noise but it was always much more subtle and could never really be heard inside the car.

I wondered if this is a normal thing or is it an early indication of something going wrong?

Is it anything like this at 49 seconds?:

https://youtu.be/OhyIEhYrx64?t=48

It's normal to hear a hiss noise with turbo cars when you've spooled a turbo up and it begins to wind down, it should sound louder the harder and longer you push the turbo and release. However were not talking Subaru loud like this: https://youtu.be/8LUoCUBLXlU?t=20. If your hearing this much then Theres something to worry about.

I can hear a hiss after pushing the turbo and releasing on both my fiesta ecoboost 125 and Alfa Giulietta, even more so after tuning them but again it nothing like the subaru example above.

Is it anything like this at 49 seconds?:

https://youtu.be/OhyIEhYrx64?t=48

It's normal to hear a hiss noise with turbo cars when you've spooled a turbo up and it begins to wind down, it should sound louder the harder and longer you push the turbo and release. However were not talking Subaru loud like this: https://youtu.be/8LUoCUBLXlU?t=20. If your hearing this much then Theres something to worry about.

I can hear a hiss after pushing the turbo and releasing on both my fiesta ecoboost 125 and Alfa Giulietta, even more so after tuning them but again it nothing like the subaru example above.

It used to be more like the videos you linked, a bit of a hiss. But this is a proper whistle, like there is a bloke hiding under the bonnet and knows to whistle when I lift off after accelerating

I don't know a lot about this engine, but perhaps there is a whistle in whichever path the 'dumped' pressure takes on lift off. I know the car has a vacuum operated waste gate, so I'm assuming this would be diverting most of the exhaust gases away from the turbo when lifting off the accelerator? So could the waste gate itself whistle?

Incidentally, the noise seems to come from the passenger lower side of the engine, but very hard to tell really so I could be completely wrong. I can't feel any change in power or smoothness of the engine. I've also checked the hoses and can't see any looseness / holes / splits. All I know is the sound has definitely changed to something much more annoying now...

I may just take it to Ford for peace of mind

Actually, thinking about this more, if it were a whistling waste gate then surely I'd hear this if I were accelerating hard (e.g. up a hill) and the boost pressure was already at it's max?

you won't hear it when accelerating, but you will when lifting off. the pressure from the turbo has to be let off, via some kind of valve - creating the whistling noise. you'll hear it best when driving with the windows down and accelerating up a hill. lift off, then you'll hear it.

it really does sound exactly like a man in your hood blowing a lollipop whistle.

you may hear the turbo whistling, getting up to speed during acceleration, too. all normal

It is indeed air release from the recirculation valve. Quite normal and more noticeable as the car gets older. It's also more noticeable with remap / Cais

Thanks for the replies guys. Strangely, the loud whistle has now gone (no changes to the car what-so-ever) and it's back to the quieter whooosh instead. Very strange, but I'll just pretend it didn't happen for the time being :)